S-8

QuickLinks -- Click here to rapidly navigate through this document

As filed with the Securities and Exchange Commission on June 20, 2003

Registration No. 333-            

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM S-8
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

NATIONAL MERCANTILE BANCORP
(Exact name of registrant as specified in its charter)

California (State or other jurisdiction of incorporation or organization)	95-3819685 (IRS Employer Identification Number)
1840 Century Park East, Los Angeles, California 90067 (Address of principal executive offices, including zip code)

NATIONAL MERCANTILE BANCORP
1996 STOCK INCENTIVE PLAN (AS AMENDED)
(Full title of the plan)

SCOTT A. MONTGOMERY, PRESIDENT AND CHIEF EXECUTIVE OFFICER
1840 Century Park East, Los Angeles, California 90230
(Name and address of agent for service)

(310) 277-2265
(Telephone number, including area code, of agent for service)

Copy to:

ALAN B. SPATZ, ESQ.
Troy & Gould Professional Corporation
1801 Century Park East, Suite 1600
Los Angeles, CA 90067-2367
(310) 553-4441

CALCULATION OF REGISTRATION FEE

Title of Securities to be Registered	Amount to be Registered(1)	Proposed Maximum Offering Price Per Share(2)	Proposed Maximum Aggregate Offering Price(2)	Amount of Registration Fee(2)
Common Stock, no par value	120,000 shares	$6.98	$837,600
Total	120,000 shares	$6.98	$837,600	$67.76

(1)

Pursuant to Rule 416(a) of the Securities Act of 1933, this Registration Statement covers, in addition to the shares of common stock specified above, an indeterminate number of additional shares of common stock that may become issuable under the National Mercantile Bancorp 1996 Incentive Stock Plan (the "Plan") as a result of the anti-dilution adjustment provisions of the Plan.

(2)

The registration fee of $67.76 for the 120,000 shares of common stock that are being registered pursuant to this Registration Statement was calculated as follows: Under the Plan, the 120,000 shares of common stock that are being registered pursuant to this Registration Statement are not the subject of outstanding options and the offering price therefore is not known; therefore, the proposed maximum offering price per share and maximum aggregate offering price were estimated in accordance with Rule 457(c) and Rule 457(h) under the Securities Act of 1933 based upon a price of $6.98, which is the average of the high and low sales prices of the common stock on the National Association of Securities Dealers Automated Quotation System on June 16, 2003.

EXPLANATORY NOTE AND INCORPORATION
OF CERTAIN INFORMATION BY REFERENCE
PURSUANT TO GENERAL INSTRUCTION E OF FORM S-8

        On July 26, 2002, National Mercantile Bancorp ("NMB") filed with the Securities and Exchange Commission a Registration Statement on Form S-8 No. 333-97131 (the "Prior Registration Statement") relating to shares of NMB's Common Stock, without par value, to be issued pursuant to NMB's 1996 Amended Stock Incentive Plan, as amended as of April 26, 2001 (the "Plan"). The Prior Registration Statement currently is effective. This Registration Statement relates to additional securities of the same class as those to which the Prior Registration Statement relates to be issued pursuant to the Plan. The contents of the Prior Registration Statement, including all exhibits thereto, are incorporated herein by reference.

        The financial statements included in the Annual Report on Form 10-KSB for the year ended December 31, 2001, incorporated herein by reference, were audited by Arthur Andersen LLP ("Andersen"). After reasonable efforts, NMB has not been able to obtain the consent of Andersen to the incorporation by reference of its audit report dated March 13, 2002 into this Registration Statement. Accordingly, NMB cannot comply with the requirement to file the consents of Andersen in reliance upon Rule 437a of the Securities Act. As a result, Andersen will not be liable to investors under Section 11(a) of the Securities Act because it has not consented to being named as an expert in this Registration Statement. Therefore, such lack of consent may limit the recovery by investors from Andersen. However, NMB did receive a letter of assurances from Arthur Anderson, which was filed as an exhibit to the Form 10-KSB for the year ended December 31, 2001, and which is incorporated herein by reference (and filed as an exhibit hereto).

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 8. Exhibits.

See the attached Exhibit Index that follows the signature pages, which is incorporated by reference.

2

SIGNATURES

        Pursuant to the requirements of the Securities Act, NMB certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in Los Angeles, State of California, on this 30th day of May, 2003.

NATIONAL MERCANTILE BANCORP
By:	/s/  SCOTT A. MONTGOMERY Scott A. Montgomery President and Chief Executive Officer

POWER OF ATTORNEY

        Each person whose signature appears below hereby constitutes and appoints Scott A. Montgomery such person's true and lawful attorney-in-fact and agent, with full power of substitution, to sign on such person's behalf, individually and in each capacity stated below, all amendments and post-effective amendments to this Registration Statement on Form S-8 and to file the same, with all exhibits thereto and any other documents in connection therewith, with the Commission under the Securities Act, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully and to all intents and purposes as each might or could do in person, hereby ratifying and confirming each act that said attorney-in-fact and agent may lawfully do or cause to be done by virtue thereof. Pursuant to the requirements of the Securities Act, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/s/  SCOTT A. MONTGOMERY Scott A. Montgomery	President and Chief Executive Officer, Director	May 30, 2003
/s/  DONALD E. BENSON Donald E. Benson	Director	May 30, 2003
/s/  JOSEPH N. COHEN Joseph N. Cohen	Director	May 30, 2003
/s/  ROBERT E. GIPSON Robert E. Gipson	Chairman	May 30, 2003
/s/  ANTIONETTE HUBENETTE, M.D. Antionette Hubenette, M.D.	Director	May 30, 2003
/s/  DION G. MORROW Dion G. Morrow	Director	May 30, 2003
/s/  CARL. R. TERZIAN Carl. R. Terzian	Director	May 30, 2003
/s/  ROBERT E. THOMSON Robert E. Thomson	Director	May 30, 2003

3

EXHIBIT INDEX

Exhibit No.	Exhibit Description
4.1	National Mercantile Bancorp 1996 Incentive Stock Plan, as amended.
5.1	Opinion of Troy & Gould Professional Corporation with respect to the securities being registered.
23.1	Consent of Troy & Gould Professional Corporation (contained in Exhibit 5.1).
23.2	Consent of Ernst & Young, L.P.
23.3	Consent of Arthur Andersen, LLP (omitted pursuant to Rule 437a of the Securities Act of 1933, as amended).
23.4	Confirmation of Receipt of Assurances from Arthur Andersen, L.L.P., dated March 14, 2002.
24.1	Power of attorney (contained on the signature page hereto).

4

QuickLinks

EXPLANATORY NOTE AND INCORPORATION OF CERTAIN INFORMATION BY REFERENCE
PART II INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 8. Exhibits.

SIGNATURES
POWER OF ATTORNEY
EXHIBIT INDEX

EX-4.1

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 4.1

NATIONAL MERCANTILE BANCORP
AMENDED 1996 STOCK INCENTIVE PLAN
(As Amended through May 29, 2003)

        Section 1.    PURPOSE    

        The purpose of the 1996 Stock Incentive Plan (the "1996 Plan") of National Mercantile Bancorp, a California corporation and a registered bank holding company under the Bank Holding Company Act of 1956, as amended (the "Company"), is to enable the Company to attract, retain and motivate its employees and independent contractors by providing for or increasing the proprietary interests of such employees and independent contractors in the Company, and to enable the Company to attract, retain and motivate its nonemployee directors and further align their interest with those of the shareholders of the Company by providing for or increasing the proprietary interest of such directors in the Company.

        Section 2.    PERSONS ELIGIBLE    

        Each director, officer, employee or independent contractor of the Company or any of its subsidiaries (each, a "Participant") shall be eligible to be considered for the grant of an Award (as hereinafter defined) under the 1996 Plan. Directors who are not employees ("Nonemployee Directors") may receive awards in addition to those described under Section 10 of the 1996 Plan.

        Section 3.    AWARDS    

        (a)   The Administrator (as hereinafter defined) responsible for administration of the 1996 Plan is authorized to enter into any type of arrangement on behalf of the Company with a Participant that is not inconsistent with the provisions of the 1996 Plan and that, by its terms, involves or might involve the issuance of (i) shares of common stock of the Company ("Common Shares") or (ii) Derivative Security (as such term is defined in Rule 16a-1 promulgated under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), as such rule may be amended from time to time) with an exercise or conversion privilege at a price related to the Common Shares or with a value derived from the value of the Common Shares. The entering into of any such arrangement is referred to herein as the grant of an "Award."

        (b)   Awards are not restricted to any specified form or structure and may include, without limitation, sales or bonuses of stock, restricted stock, stock options, reload stock options, stock purchase warrants, other rights to acquire stock, securities convertible into or redeemable for stock, stock appreciation rights, phantom stock, dividend equivalents, performance units or performance shares, and an Award may consist of one such security or benefit, or two or more of them in tandem or in the alternative.

        (c)   Awards may be issued, and Common Shares may be issued pursuant to an Award, for any lawful consideration as determined by the Administrator, including, without limitation, services rendered by the recipient of such Award.

        (d)   Subject to the provisions of the 1996 Plan, the Administrator, in its sole and absolute discretion, shall determine all of the terms and conditions of each Award granted hereunder, which terms and conditions may include, among other things:

        (i)    a provision permitting the recipient of such Award, including any recipient who is a director or officer of the Company, to pay the purchase price of the Common Shares or other

1

property issuable pursuant to such Award, or such recipient's tax withholding obligation with respect to such issuance, in whole or in part, by any one or more of the following:

        (A)  the delivery of cash;

        (B)  the delivery of other property deemed acceptable by the Administrator;

        (C)  the delivery of previously owned shares of capital stock of the Company (including "pyramiding"); or

        (D)  a reduction in the amount of Common Shares or other property otherwise issuable pursuant to such Award.

        (ii)   a provision conditioning or accelerating the receipt of benefits pursuant to such Award, either automatically or in the discretion of the Administrator, upon the occurrence of specified events, including, without limitation, a change of control of the Company (as defined by the Administrator), an acquisition of a specified percentage of the voting power of the Company, the dissolution or liquidation of the Company, a sale of substantially all of the property and assets of the Company or an event of the type described in Section 7 hereof; or

        (iii)  a provision required in order for such Award to qualify as an incentive stock option (an "Incentive Stock Option") under Section 422 of the Internal Revenue Code of 1986, as amended (the "Code"); provided, however, that no Award issued to any Nonemployee Director or any independent contractor of the Company shall qualify as an Incentive Stock Option.

        Section 4.    STOCK SUBJECT TO THE 1996 PLAN    

        (a)   At any time, the aggregate number of Common Shares issued or issuable pursuant to all Awards (including all Incentive Stock Options) granted under the 1996 Plan shall not exceed 668,510 shares subject to adjustment as provided in Section 7 hereof.

        (b)   For purposes of Section 4(a) hereof, the aggregate number of Common Shares issued or issuable pursuant to Awards granted under the 1996 Plan shall at any time be deemed to be equal to the sum of the following:

        (i)    the number of Common Shares that were issued prior to such time pursuant to Awards granted under the 1996 Plan, other than Common Shares that were subsequently reacquired by the Company pursuant to the terms and conditions of such Awards and with respect to which the holder thereof received no benefits of ownership such as dividends; plus

        (ii)   the number of Common Shares that were otherwise issuable prior to such time pursuant to Awards granted under the 1996 Plan, but that were withheld by the Company as payment of the purchase price of the Common Shares issued pursuant to such Awards or as payment of the recipient's tax withholding obligation with respect to such issuance; plus

        (iii)  the maximum number of Common Shares that are or may be issuable at or after such time pursuant to Awards granted under the 1996 Plan prior to such time.

        (c)   No Participant shall be granted Awards during any 12-month period covering more than 250,000 Common Shares.

        Section 5.    DURATION    

        Unless sooner terminated pursuant to Section 8 below, the 1996 Plan shall terminate on March 28, 2006. No Awards shall be granted under the 1996 Plan while the 1996 Plan is suspended or after it is terminated.

2

        Section 6.    ADMINISTRATION    

        (a)   The 1996 Plan shall be administered by the Board of Directors of the Company (the "Board") or by a committee (the "Committee") to which administration of the 1996 Plan, or of part of the Plan, is delegated by the Board (in either case, the "Administrator"). The Board shall appoint and remove members of the Committee in its discretion in accordance with applicable laws. At Board's discretion, the Committee may be comprised solely of "non-employee directors" within the meaning of Rule 16b-3 under the Exchange Act and/or "outside directors" within the meaning of Section 162(m) of the Code. The foregoing notwithstanding, the Administrator may delegate nondiscretionary administrative duties to such employees of the Company as it deems proper and the Board, in its absolute discretion, may at any time and from time to time exercise any and all rights and duties of the Administrator under the 1996 Plan. Notwithstanding any provision in the 1996 Plan to the contrary, in the event that the Administrator is acting with respect to an Award granted or to be granted to a member of the Board, such Board member shall abstain from any vote taken by the Board or the Committee with respect to such Award (or, if such Board member does vote on the matter, his vote will not be counted in determining whether the matter in question has been approved).

        (b)   Subject to the other provisions of the 1996 Plan, the Administrator shall have the authority, in its discretion: (i) to grant Awards; (ii) to determine the fair market value of the Common Shares subject to Awards; (iii) to determine the exercise price of Awards granted; (iv) to determine the persons to whom, and the time or times at which, Awards shall be granted, and the number of shares subject to each Award; (v) to interpret the 1996 Plan; (vi) to prescribe, amend, and rescind rules and regulations relating to the 1996 Plan; (vii) to determine the terms and provisions of each Award granted (which need not be identical), including but not limited to, the time or times at which Awards shall be exercisable; (vii) to modify or amend any Award (with the consent of the Participant if the modification or amendment is adverse to the Participant; (ix) to defer (with the consent of the Participant) the exercise date of any Award; (x) to authorize any person to execute on behalf of the Company any instrument evidencing the grant of an Award; and (xi) to make all other determinations deemed necessary or advisable for the administration of the 1996 Plan. The Administrator may delegate nondiscretionary administrative duties to such employees of the Company as it deems proper.

        (c)   All questions of interpretation, implementation, and application of the 1996 Plan shall be determined by the Administrator. Such determinations shall be final and binding on all persons.

        Section 7.    ADJUSTMENTS    

        If the outstanding shares of the class of Company stock then subject to the 1996 Plan are increased, decreased or exchanged for or converted into cash, property or a different number or kind of securities, or if cash, property or securities are distributed in respect of such outstanding securities, in either case as a result of a reorganization, merger, consolidation, recapitalization, restructuring, reclassification, dividend (other than a regular cash dividend) or other distribution, stock split, reverse stock split or the like, or if substantially all of the property and assets of the Company are sold, then, unless the terms of such transaction shall provide otherwise, the Administrator shall make appropriate and proportionate adjustments in: (i) the number and type of shares or other securities or cash or other property that may be acquired pursuant to Awards theretofore granted under the 1996 Plan; and (ii) the maximum number and type of shares or other securities that may be issued pursuant to Awards thereafter granted under the 1996 Plan. The determination of the Administrator as to what adjustments shall be made pursuant to this section, and the extent thereof, shall be final and conclusive. No fractional shares of stock shall be issued under the 1996 Plan on account of any such adjustment.

        Section 8.    AMENDMENT AND TERMINATION    

        The Board may suspend or terminate the 1996 Plan at any time; provided, however, that no such suspension or termination shall deprive the recipient of any Award theretofore granted under the 1996

3

Plan, without the consent of such recipient, of any of his or her rights thereunder or with respect thereto.

        The Board may amend the 1996 Plan at any time and in any manner subject to the following limitations:

        (a)   No such amendment shall deprive the recipient of any Award theretofore granted under the 1996 Plan, without the consent of such recipient, of any of his or her rights thereunder or with respect thereto;

        (b)   Except as otherwise provided in Section 7 relating to adjustments upon changes in stock, no such amendment shall be effective unless approved by the affirmative vote of the holders of a majority of the outstanding shares of the Company present, represented and entitled to vote at a shareholders meeting or by the written consent of a majority of the outstanding shares of the Company where such shareholder approval is required by law or pursuant to the Articles of Incorporation or Bylaws of the Company; and

        (c)   Section 10 hereof shall not be amended more than once every six (6) months, other than to comport with changes in the Code, the Employee Retirement Income Security Act, or the rules and regulations thereunder.

        Section 9.    EFFECTIVE DATE    

        The 1996 Plan shall be effective as of June 18, 1997, the date upon which it was approved by the shareholders of the Company; provided, however, that no Common Shares may be issued under this Plan until it has been approved, directly or indirectly, by the affirmative vote of the holders (the "Shareholders") of a majority of the outstanding shares of the Company present, or represented, and entitled to vote at a meeting duly held in accordance with the laws of the State of California.

        Section 10.    NONEMPLOYEE DIRECTOR OPTIONS    

        (a)   Any person elected or appointed to serve as a Nonemployee Director who has not previously served as a Nonemployee Director of the Company on or prior to October 1, 1996, shall be granted, on the first business day following the later of the date of such election or appointment or the date the 1996 Plan is approved by the Shareholders, an option to purchase 1,100 Common Shares without the requirement of any further action by the Administrator. On the first business day following the date of the annual meeting of shareholders of the Company held in 1998, or any adjournment thereof (the "1998 Meeting"), any person who was a Nonemployee Director on or after the effective date of the 1996 Plan and who is re-elected to the Board at the 1998 Meeting shall be granted an option to purchase 550 Common Shares without the requirement of any further action by the Administrator. Options that may be granted to newly-elected Nonemployee Directors or to re-elected Nonemployee Directors under this Section 10 shall be referred to collectively as the "Nonemployee Director Options." The date on which a Nonemployee Director Option is granted shall be the Date of Grant for such option.

        (b)   If, on any date upon which Nonemployee Director Options are to be automatically granted pursuant to this Section 10, the number of Common Shares remaining available for options under the 1996 Plan is insufficient for the grant to each Nonemployee Director entitled thereto of a Nonemployee Director Option to purchase the entire number of Common Shares specified in this Section 10, then a Nonemployee Director Option to purchase a proportionate amount of such available number of Common Shares (rounded to the nearest whole share) shall be granted to each Nonemployee Director entitled thereto on such date.

        (c)   Each Nonemployee Director Option granted under the 1996 Plan shall become fully exercisable one year from the Date of Grant, provided that in the event that a Change of Control (as

4

defined below) shall occur, such granted Nonemployee Director Option shall be immediately exercisable.

        (d)   Each Nonemployee Director Option granted under the 1996 Plan shall expire upon the sixth anniversary of the Date of Grant.

        (e)   Each Nonemployee Director Option shall have an exercise price equal to the aggregate Fair Market Value on the Date of Grant of the Common Shares subject thereto.

        (f)    Payment of the exercise price of any Nonemployee Director Option granted under the 1996 Plan shall be made in full in cash concurrently with the exercise of such option; provided however, that, in the discretion of the Administrator, the payment of such exercise price may instead be made:

        (i)    in whole or in part, with Common Shares delivered concurrently with such exercise (such shares to be valued on the basis of the Fair Market Value of such shares on the date of such exercise), provided that the Company is not then prohibited from purchasing or acquiring Common Shares; or

        (ii)   in whole or in part, by the delivery, concurrently with such exercise and in accordance with Section 220.3(e)(4) of Regulation T promulgated under the Exchange Act, of a properly executed exercise notice for such option and irrevocable instructions to a broker promptly to deliver to the Company a specified dollar amount of the proceeds of a sale of or a loan secured by the Common Shares issuable upon exercise of such option.

        (g)   For purposes of this Section 10, the "Fair Market Value" of a Common Share or other security on any date (the "Determination Date") shall be equal to the average of the high bid and low asked prices per Common Share or unit of such other security on the business day immediately preceding the Determination Date in the market where the security is traded, or, if the Common Shares or such other security were not quoted by any such organization on such immediately preceding business day, as determined by the Administrator. For purposes of this Section 10, the term "Change of Control" shall mean the occurrence of either of the following events: (a) the Company consolidates with or merges with or into any person or conveys, transfers or leases all or substantially all of its assets to any person, or any corporation consolidates with or merges into or with the Company in any event pursuant to a transaction in which the outstanding voting stock or units of the Company is changed into or exchanged for cash, securities or other property, other than any such transaction where the outstanding voting stock or units of the Company is not changed or exchanged at all (except to the extent necessary to reflect a change in the jurisdiction of incorporation or organization of the Company) or where the outstanding voting stock or units of the Company is changed into or exchanged for voting stock or units of the surviving corporation or organization which is not redeemable, or no "person" or "group" owns immediately after such transaction, directly or indirectly, an amount of outstanding voting stock or units necessary to effect the change of control of, or influence over, the surviving corporation or organization, as the case may be, or (b) the Company is liquidated or dissolved or adopts a plan of liquidation or dissolution.

        (h)   Each Nonemployee Director Option shall be nontransferable by the optionee other than by will or the laws of descent and distribution, and shall be exercisable during the optionee's lifetime only by the optionee or the optionee's guardian or legal representative.

        (i)    Nonemployee Director Options are not intended to qualify as Incentive Stock Options.

        (j)    Any options granted to Nonemployee Directors in addition to the automatic options granted under Section 10(a) shall be considered "Nonemployee Director Options" for purposes of this Section 10. June 20, 2003

5

QuickLinks

Exhibit 4.1

AMENDED 1996 STOCK INCENTIVE PLAN

EX-5.1

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 5.1

[TROY & GOULD LETTERHEAD]

June 20, 2003

National Mercantile Bancorp
1840 Century Park East
Los Angeles, California 90067 1615-2

Re:

Registration Statement on Form S-8

Ladies and Gentlemen:

        We have acted as counsel to National Mercantile Bancorp California (the "Company"), in connection with a Registration Statement on Form S-8 (the "Registration Statement") that the Company intends to file with the Securities and Exchange Commission (the "Commission") under the Securities Act of 1933, as amended (the "Securities Act"), on or about June 20, 2003 for the purpose of registering the offer and sale of up to 120,000 shares (the "Shares") of its common stock, no par value, which are issuable under the Company's 1996 Incentive Stock Plan, as amended (the "Stock Plan"). This opinion letter is being given to you pursuant to your request.

        As a basis for rendering our opinion expressed below, we have reviewed originals or copies of originals, certified or otherwise identified to our satisfaction, of (i) the Registration Statement, (ii) the Stock Plan, (iii) the Company's Articles of Incorporation and Bylaws, each as amended to date, (iv) resolutions of the Company's Board of Directors pertaining to the issuance of the Shares, the Registration Statement and related matters, and (v) such other certificates of public officials, certificates of officers of the Company and other documents as we have considered necessary or appropriate as a basis for rendering our opinion.

        As to questions of fact relevant to our opinion, we have relied (without any independent investigation or inquiry by us) upon certificates and statements of the Company, officers of the Company and public officials. Furthermore, in order to render our opinion, we have made and relied upon such customary assumptions as we have deemed necessary or appropriate. Among other things and in addition to any other assumptions that are described in this opinion letter, we have made and are relying upon the following assumptions, all without any independent investigation or inquiry by us:

        A.    All signatures on documents reviewed by us are genuine; all documents submitted to us as originals are authentic; and all documents submitted to us as copies conform to the originals of such documents, and such originals are authentic.

        B.    All factual representations and other statements regarding factual matters that are contained in the certificates of officers of the Company that we have examined are true and correct, and all factual representations and other statements regarding factual matters made by the Company that are contained in the Registration Statement are true and correct.

        C.    The Company will issue each of the Shares for legally sufficient consideration under the General Corporation Law of the State of California and in accordance with the terms and conditions of the Stock Plan and the Registration Statement.

        We have made such investigations of law as we have deemed necessary or appropriate as a basis for rendering our opinion, although we have not examined any laws other than the laws of the State of California. Accordingly, we neither express nor imply any opinion with respect to the laws of any other jurisdiction, and we assume no responsibility with respect to the application or effect of the laws of any other jurisdiction.

        This opinion letter is limited to the opinion expressly stated below, does not include any implied opinions and is rendered as of the date hereof. We do not undertake to advise you of matters that may come to our attention subsequent to the date hereof and that may affect our opinion, including, without limitation, future changes in applicable law.

        Based upon and subject to all of the foregoing and any and all other qualifications, limitations and assumptions that are set forth below, we are of the opinion that all Shares which are issued, delivered and paid for in accordance with the terms and conditions of the Registration Statement and the Stock Plan will be validly issued, fully paid and nonassessable.

        We consent to the filing of this opinion letter as an exhibit to the Registration Statement. However, by giving you this opinion letter and consent, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.

Very truly yours,

/s/  TROY & GOULD PROFESSIONAL CORPORATION TROY & GOULD
PROFESSIONAL CORPORATION

2

QuickLinks

Exhibit 5.1

EX-23.2

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 23.2

Consent of Independent Auditors

We consent to the incorporation by reference in the Registration Statement (Form S-8 No. 333-                        ) of National Mercantile Bancorp and Subsidiaries of our report dated February 14, 2003, with respect to the consolidated financial statements of National Mercantile Bancorp and Subsidiaries included in its Form 10-KSB for the year ended December 31, 2002, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Los Angeles, California
June 17, 2003

QuickLinks

Exhibit 23.2

Consent of Independent Auditors

EX-23.4

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 23.4

March 14, 2002

Shareholders and Board of Directors of
National Mercantile Bancorp and Subsidiaries

We represent that this audit was subject to our quality control system for the U.S. accounting and auditing practice to provide reasonable assurance that the engagement was conducted in compliance with professional standards, that there was appropriate continuity of Arthur Andersen personnel working on the audit and availability of national office consultation. Availability of personnel at foreign affiliates of Arthur Andersen is not relevant to this audit.

/s/ Arthur Andersen LLP

QuickLinks

Exhibit 23.4