UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-Q/A

Amendment No. 1

(MARK ONE)

FOR THE QUARTERLY PERIOD ENDED: September 30, 2010

COMMISSION FILE NUMBER 000-28009

RAINMAKER SYSTEMS, INC.

(Exact name of registrant as specified in its charter)

900 East Hamilton Ave., Suite 400

Campbell, California 95008

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code: (408) 626-3800

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.

(1)    Yes  x    No  ¨

(2)    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  ¨                                                 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 the 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  ¨    No  x

As of February 25, 2011, the registrant had 23,278,311 shares of Common Stock outstanding.

RAINMAKER SYSTEMS, INC.

AMENDMENT NO. 1 TO QUARTERLY REPORT ON FORM 10-Q/A

Explanatory Note

Rainmaker Systems, Inc. (the “Company”) is filing this Amendment No. 1 on Form 10-Q/A (this “Amendment”) to its Quarterly Report on Form 10-Q for the fiscal quarter ended September 30, 2010, originally filed with the Securities and Exchange Commission (the “Commission”) on November 12, 2010 (the “Original Form 10-Q”), in response to comments received from the Commission in connection with a request for confidential treatment of certain portions of Exhibit 10.1 to the Original Form 10-Q. Item 6 of Part II of the Original Form 10-Q is hereby amended to add footnote (1) to the exhibit index and to add a revised redacted version of Exhibit 10.1, which is being filed herewith. In addition, in connection with the filing of this Amendment, and pursuant to the rules of the Commission, the Company has included with this Amendment certain currently dated certifications. Except as described above, no other changes have been made to the Original Form 10-Q. This Amendment speaks as of the original filing date of the Original Form 10-Q and does not reflect any events that occurred at a date subsequent to the filing of the Original Form 10-Q or modify or update the disclosures therein in any way, except as expressly set forth herein.

PART II.—OTHER INFORMATION

The following exhibits are filed with this report as indicated below:

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.