UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K/A

(Amendment No. 1)

For the fiscal year ended March 31, 2012

OR

For the Transition Period from                to                

Commission file number 000-19672

American Superconductor Corporation

(Exact Name of Registrant as Specified in Its Charter)

Registrant’s telephone number, including area code:

(978) 842-3000

Securities registered pursuant to Section 12(b) of the Act:

Common Stock, $0.01 par value, NASDAQ Global Select Market

Securities registered pursuant to Section 12(g) of the Act:

None

Indicate by checkmark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  ¨    No  þ

Indicate by checkmark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    Yes  ¨    No  þ

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  þ    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  þ    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§ 232.405) is not contained herein, and will not be contained, to the best of the Registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  þ

Indicate by checkmark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definition of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act (Check one):

Indicate by checkmark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    Yes  ¨    No  þ

The aggregate market value of the registrant’s Common Stock held by non-affiliates of the registrant on September 30, 2011, based on the closing price of the shares of Common Stock on the Nasdaq Global Select Market on that date ($3.93 per share) was $149.2 million.

Number of shares outstanding of the registrant’s Common Stock, as of May 29, 2012 was 51,994,311.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the definitive proxy statement for the annual meeting of stockholders scheduled to be held on July 27, 2012, to be filed with the Securities and Exchange Commission (the “SEC”), are incorporated by reference in answer to Part III of this Form 10-K.

EXPLANATORY NOTE

American Superconductor Corporation (the “Company”) is filing this Amendment No. 1 to its Annual Report on Form 10-K (this “Form 10-K/A”) to amend its Annual Report on Form 10-K for the fiscal year ended March 31, 2012, as filed with the Securities and Exchange Commission (“SEC”) on June 6, 2012 (the “Original Form 10-K”). This amendment is being filed solely to file amended certifications of the Company’s Principal Executive Officer and Principal Financial Officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 to correct a typographical error that appeared in the certifications filed with the Original Form 10-K, which inadvertently referred to an incorrect date. This Form 10-K/A amends and restates in its entirety Item 15 and the Exhibit Index of the Original Form 10-K. Except as noted above, this Form 10-K/A does not update or modify any disclosures in or reflect any events occurring after the filing of the Original Form 10-K. Accordingly, this Form 10-K/A should be read in conjunction with the Original Form 10-K.

PART IV

(a) Document filed as part of this Annual Report on Form 10-K:

1. Financial Statements

The following financial statements of American Superconductor Corporation, supplemental information and report of independent registered public accounting firm required by this item are included in Item 8, “Financial Statements and Supplementary Data,” in this Form 10-K:

2. Financial Statement Schedules

See “Schedule II — Valuation and Qualifying Accounts” for the fiscal years ended March 31, 2012, 2011, and 2010. All other schedules are omitted because they are not applicable, not required or the required information is shown in the consolidated financial statements or notes thereto.

3. Exhibits Required by Item 601 of Regulation S-K under the Exchange Act.

See (b) Exhibits.

(b) Exhibits

The list of Exhibits filed as a part of this Annual Report on Form 10-K is set forth on the Exhibit Index immediately preceding such Exhibits, and is incorporated herein by reference.

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American Superconductor Corporation

Schedule II — Valuation and Qualifying Accounts

(In thousands)

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SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

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EXHIBIT INDEX

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