UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K/A

(Amendment No. 1)

For the fiscal year ended July 31, 2011

For the transition period from                     to                     

Commission file number: 001-33347

Aruba Networks, Inc.

(Exact name of registrant as specified in its charter)

1344 Crossman Ave.

Sunnyvale, California 94089-1113

(408) 227-4500

(Address, including zip code, and telephone number,

including area code, of registrant’s principal executive offices)

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

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

None

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 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 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, 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. (Check one):

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

As of January 31, 2011, the last business day of the registrant’s most recently completed second fiscal quarter, the aggregate market value of the registrant’s common stock held by non-affiliates was approximately $2,063,670,475, based on the closing price of such stock reported for such date on the NASDAQ Global Select Market. This calculation does not reflect a determination that persons are affiliates for any other purposes.

The number of outstanding shares of the registrant’s common stock was 105,678,491 as of September 14, 2011.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s Proxy Statement for the 2011 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s fiscal year ended July 31, 2011 are incorporated by reference into Part III of this Annual Report on Form 10-K.

EXPLANATORY NOTE

We filed our Annual Report on Form 10-K for the fiscal year ended July 31, 2011 (the “Form 10-K”) with the Securities and Exchange Commission (the “SEC”) on September 27, 2011. We are filing this Amendment No. 1 to the Form 10-K (this “Form 10-K/A”) in response to communications with the SEC in connection with a request for confidential treatment under Rule 24b-2 promulgated under the Securities and Exchange Act of 1934, as amended (the “Exchange Act”), with respect to Exhibit 10.47 originally filed with the Form 10-K. The sole purpose of this Form 10-K/A is to file a revised redacted version of Exhibit 10.47, which supersedes in its entirety the Exhibit 10.47 as originally filed with the Form 10-K. Certain portions of the information that were omitted from Exhibit 10.47 as filed with the Form 10-K have now been included as part of the revised Exhibit 10.47. To accomplish the foregoing, this Form 10-K/A hereby amends and restates in its entirety Item 15 of Part IV of the Form 10-K.

Pursuant to Rule 12b-15 under the Exchange Act, this Form 10-K/A also contains new certifications pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. Accordingly, Item 15 of Part IV has also been amended and restated in its entirety to include the currently dated certifications as exhibits. Because no financial statements have been included in this Form 10-K/A and this Form 10-K/A does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation S-K, paragraphs 3, 4 and 5 of the certifications have been omitted.

No attempt has been made in this Form 10-K/A to modify or update the other disclosures presented in the Form 10-K, including, without limitation, the financial statements. This Form 10-K/A does not reflect events occurring after the filing of the Form 10-K or modify or update the disclosures in the Form 10-K, except as set forth in this Form 10-K/A, and should be read in conjunction with the Form 10-K and our other filings with the SEC.

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PART IV

ITEM 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

(a)(1) Financial Statements: See Index to Consolidated Financial Statements in Item 8 of this report

(2) Financial Schedules: Schedule II Valuation and Qualifying Accounts appeared on page 91 of the Form 10-K and should be read in conjunction with the Consolidated Financial Statements included in this report.

Schedules not listed above have been omitted because the information required to be set forth therein is not applicable or is shown in the financial statements or notes thereto.

(b) Exhibits. The exhibits listed on the Exhibit Index on page 4 of this Form 10-K/A are included, or incorporated by reference, in this report.

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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, on the 8^th day of February 2012.

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EXHIBIT INDEX

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