Exhibit 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In accordance with 18 U.S.C. 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, Daniel Stephen Hafner, Chief Executive Officer and Cofounder of KAYAK Software Corporation (the “Registrant”), and Melissa Reiter Birge, Chief Financial Officer and Treasurer of the Registrant, each hereby certifies that, to the best of their knowledge:

1. The Registrant’s Quarterly Report on Form 10-Q for the period ended September 30, 2012, to which this Certification is attached as Exhibit 32.1 (the “Periodic Report”), fully complies with the requirements of Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934, as amended; and

2. The information contained in the Periodic Report fairly presents, in all material respects, the financial condition of the Registrant at the end of the period covered by the Periodic Report and results of operations of the Registrant for the periods covered by the Periodic Report.

Date: May 14, 2013

/s/ Daniel Stephen Hafner    

Daniel Stephen Hafner

Chief Executive Officer and Cofounder

/s/ Melissa Reiter Birge        

Melissa Reiter Birge

Chief Financial Officer and Treasurer