UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

(Amendment No. 1)

(Mark One)

FOR THE QUARTERLY PERIOD ENDED MARCH 31, 2012.

FOR THE TRANSITION PERIOD FROM              TO             .

Commission file number: 1-12619

Ralcorp Holdings, Inc.

(Exact name of registrant as specified in its charter)

(314) 877-7000

(Registrant’s telephone number, including area code)

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  x     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  x    No  ¨

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 definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):

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

Number of shares of Common Stock, $.01 par value, outstanding as of September 10, 2012: 55,032,538

EXPLANATORY NOTE

This Amendment No. 1 on Form 10-Q/A (“Form 10-Q/A”) amends the Quarterly Report on Form 10-Q of Ralcorp Holdings, Inc. for the quarter ended March 31, 2012, as originally filed with the Securities and Exchange Commission on September 12, 2012 (the “Original Filing”). As a result of a processing error, the Section 1350 Certification attached as Exhibit 32 to the Original Filing included an incorrect date. This Form 10-Q/A is being filed solely to include the correct certification.

SIGNATURES

Pursuant to the requirements 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.

Exhibit Index