EXHIBIT 5

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October 15, 2004



Securities and Exchange Commission
Judiciary Plaza
450 Fifth Street
Washington, D.C.  20549

RE:      MERCANTILE BANK CORPORATION
         2004 EMPLOYEE STOCK OPTION PLAN
         REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

         We are acting as counsel for Mercantile Bank Corporation, a Michigan
corporation ("Mercantile"), in connection with its registration on a Form S-8
Registration Statement (the "Registration Statement") of 250,000 shares of its
common stock (the "Option Shares") that will be offered pursuant to stock
options that are issued under Mercantile's 2004 Employee Stock Option Plan (the
"Plan"). This opinion is being delivered pursuant to the requirements of Item
601(b)(5) of Regulation S-K under the Securities Act of 1933.

         In connection with this opinion, we have examined originals or copies
of (i) the Plan, (ii) the Articles of Incorporation of Mercantile, (iii) the
Bylaws of Mercantile, (iv) resolutions of the Board of Directors of Mercantile
relating to the adoption of the Plan and reservation of and issuance of common
stock in connection with the Plan, and (v) such other documents as we have
deemed appropriate in connection with this opinion.

         In our examination, we have assumed the genuiness of all signatures,
the legal capacity of all natural persons signing or delivering an instrument,
the authenticity of all documents submitted to us as originals, and the
conformity to original documents of all documents submitted to us as certified
or photostatic copies. As to any facts material to this opinion that were not
independently established or verified, we have relied upon oral or written
statements and representations of officers or other representatives of
Mercantile and upon certificates or other documents of public officials.

         Upon the basis of above, we are of the opinion that the Option Shares
have been duly authorized and when issued pursuant to the Plan will be legally
issued, fully paid and non-assessable.

         We consent to the filing of this opinion as Exhibit 5 to the
Registration Statement and to the reference to our Firm's name in Item 5,
Interest of Named Experts and Counsel, of the Registration Statement. In giving
such consent, we do not admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act of 1933.


                                            Very truly yours,

                                            /s/ Dickinson Wright PLLC