UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K/A

(Amendment No. 1)

For the fiscal year ended September 30, 2007

OR

For the transition period from                      to                     

Commission file number 000-26299

ARIBA, INC.

(Exact name of registrant as specified in its charter)

(650) 390-1000

(Registrant’s telephone number, including area code)

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

None

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

Common Stock, $0.002 par value

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  ¨    No  x

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 if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K 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, or a non-accelerated filer (as defined in Rule 12b-2 of the Exchange Act).

Large accelerated filer  x                Accelerated filer  ¨                Non-accelerated filer  ¨

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

The aggregate market value of the common stock held by non-affiliates of the registrant as of March 31, 2007, the last business day of the registrant’s most recently completed second fiscal quarter (based on the closing price of $9.40 on the Nasdaq Global Market as of that date) was approximately $736.4 million.

As of October 31, 2007, there were 80,461,933 shares of the registrant’s common stock outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive proxy statement to be delivered to stockholders in connection with the 2008 annual meeting of stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K to the extent stated herein.

EXPLANATORY NOTE

This Amendment No. 1 (“Amendment No. 1”) to the Registrant’s Annual Report on Form 10-K for the fiscal year ended September 30, 2007, originally filed November 15, 2007 (the “Original Annual Report”), is being filed solely to amend the Item 15 list of exhibits and Exhibit Index. The Item 15 list of exhibits and Exhibit Index in that report did not include an Exhibit 2.2 – Amendment No. 1 to the Agreement and Plan of Merger and Reorganization, dated as of September 20, 2007, by and among Ariba, Inc., Axe Acquisition Corporation, Procuri, Inc. and Insight Venture Partners, LLC, as Stockholders’ Representative. This Amendment No. 1 is being filed to include under Item 15 list of exhibits and Exhibit Index an Exhibit 2.2. We are filing herewith currently dated certifications in Exhibit 31.1, 31.2 and 32.1. Except as described above, no other changes have been made to the Original Annual Report, and this Amendment No. 1 does not amend or update any other information contained in that original filing. No revisions have been made to the Registrant’s financial statements contained in the Original Annual Report.

(a)

3. EXHIBITS

2

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this Form 10-K/A to be signed on its behalf by the undersigned thereunto duly authorized on November 26, 2007.

Pursuant to the requirements of the Securities Exchange Act of 1934, this Form 10-K/A has been signed below by the following persons on behalf of the Registrant and in the capacities and on the dates indicated:

EXHIBIT INDEX

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