Priceline has won US antitrust approval to buy Kayak Software, the Federal Trade Commission said on Tuesday.
The acquisition, announced in early November, is valued at USD$1.8 billion.
The deal was one of several on a list of approved transactions that the FTC issues several times a week. The FTC puts out the listing, 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 USD$26. It operates like a search engine, letting consumers compare pricing along with other websites such as Priceline rivals Expedia and Orbitz.
Priceline has the largest market capitalisation 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.