UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K/A

For the fiscal year ended December 31, 2012

or

Commission File No. 001- 34280

American National Insurance Company

(Exact name of registrant as specified in its charter)

(409) 763-4661

(Registrant’s telephone number, including area code)

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

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

None

(Title of Class)

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

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

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.    x  Yes    ¨  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 (§229.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    x  Yes    ¨  No

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this chapter) is not contained herein, and will not be contained, to the best of 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.    ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definitions of “large accelerated filer”, “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act:

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

The aggregate market value on June 30, 2012 (the last business day of the registrant’s most recently completed second fiscal quarter) of the voting stock held by non-affiliates of the registrant was approximately $516.9 million. For purposes of the determination of the above-stated amount, only directors, executive officers and 10% shareholders are presumed to be affiliates, but neither the registrant nor any such person concedes that they are affiliates of registrant.

As of March 1, 2013, there were 26,898,717 shares of the registrant’s voting common stock, $1.00 par value per share, outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Information called for in Part III of this Form 10-K is incorporated by reference to the registrant’s Definitive Proxy Statement to be filed within 120 days of the close of the registrant’s fiscal year in conjunction with the registrant’s annual meeting of shareholders.

EXPLANATORY NOTE

This Form 10-K/A is being filed as Amendment No. 1 to the Form 10-K of American National Insurance Company filed with the U.S. Securities and Exchange Commission on March 8, 2013 for the purpose of amending the Consent of Independent Registered Certified Public Accounting Firm to correct a typographical error with respect to the date of such consent. There are no other changes to the consent.

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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