UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 11-K

þ ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended September 30, 2007

OR

o TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                      to                     

Commission file number 001-8137

A. Full title of the plan and the address of the plan, if
different from that of the issuer named below:

American Pacific Corporation 401(k) Plan

B. Name of the issuer of the securities held
pursuant to the plan and the address of its
principal executive office:

American Pacific Corporation
3770 Howard Hughes Parkway
Suite 300
Las Vegas, NV 89169

McGladrey & Pullen
Certified Public Accountants

American Pacific Corporation
     401(k) Plan

Financial Report
09.30.2007

McGladrey & Pullen, LLP is a member firm of RSM International
— an affiliation of separate and independent legal entities.

Contents

Independent Registered Public Accounting Firm’s Report as of and for the year ended September 30, 2007	1
Independent Registered Public Accounting Firm’s Report as of September 30, 2006	2
Financial Statements
Statements of Net Assets Available for Benefits	3
Statement of Changes in Net Assets Available for Benefits	4
Notes to Financial Statements	5 — 11
Supplemental Schedule
Form 5500, Schedule H, Part IV, Line 4i — Schedule of Assets Held at End of Year	12

McGladrey & Pullen
Certified Public Accountants

Report of Independent Registered Public Accounting Firm

To the Plan Administrator and Participants
American Pacific Corporation 401(k) Plan
Las Vegas, Nevada

We have audited the accompanying statement of net assets available for benefits of the American Pacific Corporation 401(k) Plan (the “Plan”) as of September 30, 2007 and the related statement of changes in net assets available for benefits for the year then ended. These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on these financial statements based on our audit.

We conducted our audit in accordance with auditing standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audit provides a reasonable basis for our opinion.

In our opinion, the 2007 financial statements referred to above present fairly, in all material respects, the net assets available for benefits of the Plan as of September 30, 2007, and the change in net assets available for benefits for the year then ended, in conformity with accounting principles generally accepted in the United States of America.

Our audit was made for the purpose of forming an opinion on the 2007 basic financial statements taken as a whole. The supplemental schedule of assets held at end of year as of September 30, 2007, is presented for the purpose of additional analysis and is not a required part of the basic financial statements, but is supplementary information required by the United States Department of Labor Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. This supplemental schedule is the responsibility of the Plan’s management. The supplemental schedule has been subjected to the auditing procedures applied in the audits of the basic financial statements and, in our opinion, is fairly stated in all material respects in relation to the basic financial statements taken as a whole.

As described in Note 2, the Plan adopted Financial Accounting Standards Board Staff Position AAG INV-1 and SOP 94-4-1, Reporting of Fully Benefit-Responsive Investment Contracts Held by Certain Investment Companies Subject to the AICPA Investment Company Guide and Defined-Contribution Health and Welfare and Pension Plans, as of September 30, 2007. We audited the information described in Note 2 that was applied to the 2006 financial statements. In our opinion, such information was appropriate and was properly applied.

/s/ McGladrey & Pullen, LLP
Las Vegas, Nevada
March 26, 2008

McGladrey & Pullen, LLP is a member firm of RSM International
— an affiliation of separate and independent legal entities.

1

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Trustees and Participants of the
American Pacific Corporation 401(k) Plan:

We have audited the accompanying statement of net assets available for benefits of American Pacific Corporation 401(k) Plan (the “Plan”) as of September 30, 2006. This statement of net assets available for benefits is the responsibility of the Plan’s management. Our responsibility is to express an opinion on this statement of net assets available for benefits based on our audit.

We conducted our audit in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the statement of net assets available for benefits is free of material misstatement. The Plan is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. Our audit included consideration of internal control over financial reporting as a basis for designing audit procedures that are appropriate in the circumstances, but not for the purpose of expressing an opinion on the effectiveness of the Plan’s internal control over financial reporting. Accordingly, we express no such opinion. An audit also includes examining, on a test basis, evidence supporting the amounts and disclosures in the statement of net assets available for benefits, assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall statement of net assets available for benefits presentation. We believe that our audit provides a reasonable basis for our opinion.

In our opinion, such statement of net assets available for benefits presents fairly, in all material respects, the net assets available for benefits of American Pacific Corporation 401(k) Plan as of September 30, 2006, in conformity with accounting principles generally accepted in the United States of America.

/s/ DELOITTE & TOUCHE LLP

Las Vegas, Nevada
April 16, 2007

2

American Pacific Corporation 401(k) Plan

Statements of Net Assets Available for Benefits

September 30, 2007 and 2006

	2007		2006
Assets
Investments, participant directed, at fair value:
Shares of registered investment companies	$	13,049,561	$	7,966,745
American Pacific Corporation common stock		1,725,213		828,215
Forfeiture/asset holding account		—		3,367
Participant loans		415,750		386,398
Investments, participant directed, at estimated fair value:
Common/Collective trust		—		1,910,862
		15,190,524		11,095,587
Receivables:
Profit sharing contribution		104,241		—
Net assets available for benefits	$	15,294,765	$	11,095,587

See Notes to Financial Statements.

3

American Pacific Corporation 401(k) Plan

Statement of Changes in Net Assets Available for Benefits

For the Year Ended September 30, 2007

Additions:
Investment income:
Dividend and interest income	$	572,825
Net appreciation in fair value of investments		1,749,014
Interest from loan repayments		29,526
		2,351,365
Contributions:
Participant contributions		1,608,572
Employer match contributions		464,423
Profit sharing contribution		197,152
Rollover contributions		265,871
		2,536,018
Total additions		4,887,383
Deductions:
Benefits paid		684,420
Plan expenses		3,785
Total deductions		688,205
Increase in Net Assets		4,199,178
Net assets available for benefits:
Beginning of year		11,095,587
End of year	$	15,294,765

See Notes to Financial Statements.

4

American Pacific Corporation 401(k) Plan

Notes to Financial Statements

Note 1. Plan Description

The following description of the American Pacific Corporation 401(k) Plan (the “Plan”) provides only general information. Participants should refer to the Plan document, as amended, for a complete description of the Plan’s provisions.

General

The Plan is a defined contribution plan open to all employees of American Pacific Corporation (the “Company”) and its subsidiaries who are not members of a collective bargaining unit. Employees are eligible to participate after completing at least 3 months of service and are allowed to enter the Plan on the first day of each fiscal quarter. Franklin Templeton Bank & Trust (“Franklin”) serves as the trustee of the Plan and the Company is the Plan Administrator. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”).

Contributions

Each year, participants may contribute up to the maximum allowed by the Internal Revenue Code. In addition, the Plan allows for catch up contributions by employees 50 years and older. Participants may contribute amounts representing distributions from other qualified plans, as defined in the Plan’s provisions. For the year ended September 30, 2007 employee rollover contributions totaled $265,871. The Company, at its discretion, may contribute to the Plan. For the year ended September 30, 2007, the Company elected to match contributions for employees of its subsidiaries located in New York and California only. The Company elected to make matching contributions equal to 100% of employee contributions, up to the first 3% of employee compensation, and 50% of employee contributions, up to the next 3% of employee compensation. For the year ended September 30, 2007, the Company made matching contributions of $464,423.

As of December 31, 2005, the Company elected to make an annual discretionary profit sharing contribution to eligible employees of its subsidiary located in New York of at least 3% of annual compensation. Any amount over the annual discretionary profit sharing contribution of at least 3%, will be at the discretion of the Company. For the year ended September 30, 2007, the Company made profit sharing contributions of $104,241.

5

American Pacific Corporation 401(k) Plan

Notes to Financial Statements

Note 1. Plan Description (continued)

Participant accounts

Each participant’s account is credited with the participant’s contributions, including amounts rolled over from other qualified plans, and allocations of the Company’s discretionary matching contribution, the Company’s discretionary profit sharing contribution, and Plan earnings, and is charged with benefit payments and an allocation of administrative expenses. Allocations are based on participant earnings or account balances, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s vested accounts.

Investments

Participants must direct the investment of their account balance into various investment options offered by the Plan.

Vesting

Participants are immediately vested in their contributions, rollover contributions, and employer matching contributions, plus actual earnings thereon. Vesting in the Company’s discretionary profit sharing contribution is based on years of continuous service. A participant vests 20% per year from years two through six of credited service. A participant’s interest in the Plan becomes fully vested if employment terminates due to death, total and permanent disability or retirement at age 65.

Payment of benefits

Upon termination of service, if the vested value of a participant’s account is less than $5,000, his or her account will be distributed in a single lump-sum payment. If the vested value of a participant’s account exceeds $5,000, he or she may elect to receive either a lump-sum amount, substantially equal payments or elect to have all the distribution paid in a direct rollover to another qualified plan, or a combination of the above.

Participant loans

In accordance with the provisions of the Plan, participants may borrow from their fund accounts a minimum of $1,000 up to a maximum amount equal to the lesser of $50,000 or 50% of their vested account balance. Loan transactions are treated as a transfer (to) from the investment (from) to the participant loan fund. Loan terms range from one to five years or up to ten years for the purchase of a primary residence. The loans are collateralized by the participant’s vested balance in the Plan and bear interest at prime rate plus 1%. Principal and interest is paid ratably through payroll deductions. Interest rates on participant loans vary, ranging from 5% to 10%. Maturities range from January 2008 through April 2017.

Forfeited accounts

At September 30, 2007 and 2006, forfeited accounts totaled $6,770 and $3,367, respectively. At September 30, 2007 the forfeited accounts are reported as shares of registered investment companies on the statement of net assets. Forfeited accounts are utilized first to reduce Plan expenses. Any remaining forfeitures are allocated to participants in proportion to each participant’s compensation for the year. There were no forfeitures used to reduce Plan expenses or allocated to Plan participants during the year ended September 30, 2007.

Expenses

Administrative expenses of the Plan are paid by either the Plan or the Company, as provided in the Plan document.

6

American Pacific Corporation 401(k) Plan

Notes to Financial Statements

Note 2. Summary of Significant Accounting Policies

Basis of accounting

The Plan’s financial statements are prepared on the accrual basis of accounting, except for the cash basis recording of benefits paid.

As described in Financial Accounting Standards Board Staff Position AAG INV-1 and SOP 94-4-1, Reporting of Fully Benefit-Responsive Investment Contracts Held by Certain Investment Companies Subject to the AICPA Investment Company Guide and Defined-Contribution Health and Welfare and Pension Plans (the “FSP”), investment contracts held by a defined-contribution plan are required to be reported at fair value. However, contract value is the relevant measurement attribute for that portion of the net assets available for benefits of a defined-contribution plan attributable to fully benefit-responsive investment contracts because contract value is the amount participants would receive if they were to initiate permitted transactions under the terms of the plan. During the year ended September 30, 2006, the Plan invested in an investment contract held within a common collective trust. As required by the FSP, the Statements of Net Assets Available for Benefits presents the fair value of the investment in the common collective trust as well as the adjustment of the investment in the common collective trust from fair value to contract value relating to the investment contract. The Statement of Changes in Net Assets Available for Benefits is prepared on a contract value basis. The provisions of the FSP AAG INV-1 and SOP 94-4-1 have been retroactively applied in the Statements of Net Assets Available for Benefits presented as of September 30, 2006, as required. The fair value of the investment in the common collective trust approximates the contract value for the Plan’s investment.

Use of estimates in the preparation of financial statements

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amount of assets, liabilities, and changes therein, disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Investment valuation and income recognition

Investments in shares of registered investment companies and common stock are stated at their fair value at year-end based on quoted market prices. Investments in the common/collective trust are stated at estimated fair values, which have been determined based on the unit values of the funds. Unit values are determined by dividing the fund’s net assets at fair value by its units outstanding at the valuation dates. Participant loans are valued at the outstanding loan balance.

Purchases and sales of securities are recorded on a trade-date basis. Interest income is recorded on the accrual basis. Net unrealized appreciation or depreciation for the year is reflected in the Statement of Changes in Net Assets Available for Benefits.

Payment of benefits

Benefits are recorded when paid.

7

American Pacific Corporation 401(k) Plan

Notes to Financial Statements

Note 2. Summary of Significant Accounting Policies (continued)

New accounting pronouncements

In June 2006, the Financial Accounting Standards Board (“FASB”) issued FASB Interpretation No. 48 (“FIN 48”), Accounting for Uncertainty in Income Taxes — an interpretation of FASB Statement 109. FIN 48 clarifies the accounting for uncertainty in income taxes recognized in financial statements in accordance with FASB Statement No. 109, Accounting for Income Taxes. FIN 48 prescribes a comprehensive model for recognizing, measuring, presenting and disclosing in the financial statements tax positions taken or expected to be taken on a tax return. If there are changes in net assets available for benefits as a result of application of FIN 48, these will be accounted for as an adjustment to the opening balance of net assets available for benefits. Additional disclosures about the amounts of such liabilities will be required also. In February 2008, the FASB delayed the effective date of FIN 48 for certain nonpublic enterprises to annual financial statements for fiscal years beginning after December 15, 2007. The adoption of FIN 48 is not expected to have a material impact on the Plan’s net assets, results of operations and financial statement disclosures, if any.

In addition, in September 2006, Statement of Financial Accounting Standards No. 157, Fair Value Measurements (“SFAS 157”), was issued and is effective for fiscal years beginning after November 15, 2007. SFAS 157 defines fair value, establishes a framework for measuring fair value and expands disclosures about fair value measurements. Management is in the process of evaluating the impact of the adoption of SFAS 157 will have on the Plan’s net assets, results of operations and financial statement disclosures, if any.

In February 2007, the FASB issued Statement of Financial Accounting Standards No. 159, The Fair Value Option for Financial Assets and Financial Liabilities (“SFAS 159”). SFAS 159 permits plans to elect to follow fair value accounting for certain financial assets and liabilities in an effort to mitigate volatility in earnings without having to apply complex hedge accounting provisions. The standard also establishes presentation and disclosure requirements designed to facilitate comparison between entities that choose different measurement attributes for similar types of assets and liabilities. SFAS 159 is effective for fiscal years beginning after November 15, 2007. Management is in the process of evaluating the impact of the adoption of SFAS 159 will have on the Plan’s net assets, results of operations and financial statement disclosures, if any.

8

American Pacific Corporation 401(k) Plan

Notes to the Financial Statements

Note 3. Investments

The Plan’s investments that represented 5% or more of the Plan’s net assets available for benefits as of September 30, are as follows:

	2007		2006
Common/Collective trust:
Franklin Stable Value Fund A	$	—	$	1,910,862
Shares of registered investment companies:
Franklin Cash Reserves Fund Inst	$	2,521,890		**
Franklin Growth Fund A	$	1,466,797	$	1,045,567
Franklin Equity Income Fund A	$	1,252,911	$	1,032,502
Mutual Discovery Fund A	$	1,926,665	$	1,160,285
Mutual Shares Fund A	$	1,264,128	$	1,040,342
Allianz CCM Mid Cap Fund A		**	$	567,255
DWS Equity 500 Index Fund		**	$	639,246
Franklin Rising Dividend Fund A		**	$	623,882
Common stock:
American Pacific Corporation common stock	$	1,725,213	$	828,215

** These investments are below 5% of the Plan’s net assets at September 30, 2007 or September 30, 2006.

9

American Pacific Corporation 401(k) Plan

Notes to the Financial Statements

Note 3. Investments (continued)

The Plan’s investments (including gains and losses on investments bought and sold, as well as held during the year, appreciated (depreciated) in value during the year ended September 30, 2007 as follows:

Shares of registered investment companies:
Aim Small Cap Fund A	$	100,154
Allianz CCM Mid Cap Fund A		72,392
Dreyfus Small Cap Index Fund		303
DWS Equity 500 Index Fund		93,634
Franklin Equity Income Fund A		30,900
Franklin Growth Fund A		205,333
Franklin High Income Fund A		(357	)
Franklin Real Estate Securities Fund A		(61,052	)
Franklin Rising Dividend Fund A		25,146
Franklin Small Mid Cap Growth Fund A		(15,174	)
Franklin Technology Fund A		39,545
Franklin Templeton Growth Target Fund A		5,025
Franklin Total Return Fund A		(155	)
Franklin US Government Fund A		(1,118	)
Franklin Utilities Fund A		33,085
Franklin Utilities Fund R		(69	)
Mutual Discovery Fund A		230,181
Mutual Shares Fund A		69,430
Franklin Small Cap Value Fund A		10,836
Franklin Cash Reserves Fund Inst		159
Employer Stock Awaiting Purchase Fund		80
Common stock:
American Pacific Corporation common stock		910,736
Net appreciation in fair value of investments	$	1,749,014

10

American Pacific Corporation 401(k) Plan

Notes to the Financial Statements

Note 4. Plan Termination

Although it has not expressed any intention to do so, the Company has the right under the Plan to discontinue its contributions at any time and to terminate the Plan subject to the provisions set forth in ERISA. In the event of Plan termination, participants would become 100% vested in their account.

Note 5. Income Tax Status

The Plan uses a volume submitter plan document sponsored by Franklin Templeton Investments. The Internal Revenue Service (“IRS”) has determined and informed the volume submitter sponsor by a letter dated September 4, 2001 that the volume submitter plan is designed in accordance with applicable sections of the Internal Revenue Code (“IRC”).

The Plan itself is not required to and has not been submitted to the IRS for a determination that the Plan is designed in accordance with the IRC. In addition, the Plan has been amended since the IRS letter of September 4, 2001. However, the Plan administrator and the Plan’s management believe that the Plan is designed and is currently being operated in compliance with the applicable requirements of the IRC and the related trust was exempt from taxation as of the financial statement date.

Note 6. Exempt Party-In-Interest Transactions

Certain Plan investments are shares of mutual funds managed by Franklin or its affiliates. Franklin is the trustee as defined by the Plan and, therefore, these transactions qualify as party-in-interest transactions. Fees paid by the Plan to Franklin totaled $3,785 for the year ended September 30, 2007.

At September 30, 2007 and 2006, the Plan held 110,449 and 108,263 shares of common stock of the Company, respectively, with a cost basis of $981,672 and $836,540, respectively. At September 30, 2007 and 2006, the Plan held 16,090 and 15,028 units in the Employer Stock Awaiting Purchase Fund, respectively, with a cost basis of $16,090 and $15,028, respectively.

Note 7. Risk and Uncertainties

The Plan utilizes various investment instruments. Investment securities, in general, are exposed to various risks, such as interest rate, credit and overall market volatility. Due to the level or risk associate with certain investment securities, it is reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect the amounts reported in the accompanying financial statements.

Note 8. Subsequent Event

Effective October 2007, the Company appointed Orchard Trust Company, LLC as trustee and custodian and Great-West Retirement Services as recordkeeper of the Plan.

11

American Pacific Corporation 401(k) Plan

Form 5500, Schedule H, Part IV, Line 4i — Schedule of Assets Held at End of Year
September 30, 2007

		Description of Investment, including
	Identity of issuer, borrower, lessor, or similar	maturity date, collateral and maturity
	party	value	Cost	Current Value
	Shares of registered invesment companies:
*	Franklin Cash Reserves Fund Inst	Mutual fund	**	$	2,521,890
*	Mutual Discovery Fund A	Mutual fund	**		1,926,665
*	Franklin Growth Fund A	Mutual fund	**		1,466,797
*	Mutual Shares Fund A	Mutual fund	**		1,264,128
*	Franklin Equity Income Fund A	Mutual fund	**		1,252,911
*	Franklin Rising Dividend Fund A	Mutual fund	**		757,143
*	DWS Equity 500 Index Fund	Mutual fund	**		720,234
*	Allianz CCM Mid Cap Fund A	Mutual fund	**		716,378
*	Aim Small Cap Growth Fund A	Mutual fund	**		700,089
*	Franklin Small Cap Value Fund A	Mutual fund	**		309,849
*	Franklin Utilities Fund A	Mutual fund	**		289,390
*	Franklin Total Return Fund A	Mutual fund	**		261,996
*	Franklin US Government Fund A	Mutual fund	**		238,034
*	Franklin Real Estate Securities Fund A	Mutual fund	**		216,188
*	Franklin Technology Fund A	Mutual fund	**		180,731
*	Franklin High Income Fund A	Mutual fund	**		124,929
*	Franklin Templeton Growth Target Fund A	Mutual fund	**		69,923
*	Dreyfus Small Cap Index Fund	Mutual fund	**		16,196
*	Employer Stock Awaiting Purchase Fund	Mutual fund	**		16,090
					13,049,561
*	American Pacific Corporation Common Stock	Common Stock (110,449 Shares)	**		1,725,213
*	Participant Loans Receivable	Interest rates ranging from
		5% -10%, maturing through April 2017	**		415,750
	Total investments			$	15,190,524

*	Represents a party-in-interest to the Plan.
**	Cost information is not required for participant-directred investments and, therefore, is not included.

12

SIGNATURES

The Plan. Pursuant to the requirements of the Securities and Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.

	American Pacific Corporation 401(k) Plan
	By:	American Pacific Corporation, as Plan
		Administrator
Date: March 28, 2008	By:	/s/ JOHN R. GIBSON
		John R. Gibson
		Chairman & Chief Executive Officer

EXHIBIT INDEX

Exhibit
Index	Description
23.1	Consent of Independent Registered Public Accounting Firm – McGladrey & Pullen, LLP
23.2	Consent of Independent Registered Public Accounting Firm – Deloitte & Touche LLP