The acquisition, announced in early November, is valued at $1.8 billion.
The deal was one of several on a list of approved transactions that the FTC issues several times a week. The listing is put out by the FTC, but the approvals could come from either that agency or the Justice Department.
Kayak, which offers a website and mobile applications to help consumers compare prices for airlines, hotels and rental cars, went public in July with shares priced at $26. It operates like a search engine, letting consumers compare pricing along with other websites such as Priceline.com rivals Expedia Inc and Orbitz Worldwide Inc.
Priceline, which is known for its name-your-own-price auction, has the largest market capitalization of online travel agencies.
Kayak will be operated independently under the leadership of its current management, which includes company co-founders Steve Hafner and Paul English, Priceline said in November.
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