The Justice Department said that a review of the transaction by its antitrust division had concluded that it was "not likely to substantially lessen competition in the sale of display advertising."
"Although the Antitrust Division concluded that this particular transaction was unlikely to cause consumer harm, the division will continue to be vigilant in the enforcement of the antitrust laws to protect competition in display and other forms of online advertising," the department said in a statement.
Google announced the acquisition of Admeld in June. The exact purchase price was not revealed but various reports put it at around $400 million.
Mountain View, California-based Google makes most of its money from advertising tied to Internet search but is seeking to carve out a bigger slice of the market for display advertising, which includes rich media, digital video and banner ads.
According to the Interactive Advertising Bureau and PricewaterhouseCoopers, US online advertising revenue rose 15 percent last year to a record $26 billion with display ads accounting for 38 percent of the total.
According to digital marketing firm eMarketer, Facebook is on track to pass Yahoo! in US display advertising revenue this year while Google will also gain market share.
Facebook's share of US online display ad revenue will grow to 17.7 percent this year, up from 12.2 percent last year, while Yahoo!'s share is expected to decline to 13.1 percent in 2011 from 14.4 percent last year, eMarketer said.
Google's share of US display advertising revenue will grow to 9.3 percent this year from 8.6 percent last year, eMarketer said.
Google has come in for increasing regulatory review in the United States and Europe as it has grown from a scrappy startup into an Internet titan.
Among the deals that have drawn scrutiny are Google's $3.1 billion purchase of online ad firm DoubleClick, its $750 million buy of mobile ad network AdMob and its $700 million acquisition of flight data company ITA Software.
In 2008, Google was forced to drop plans for a joint search advertising partnership with Yahoo! amid opposition from the Justice Department. Google is also currently cooperating with a US Federal Trade Commission probe into its search and advertising business.
Founded in 2007, Admeld describes its mission on its website as providing publishers with "the cutting edge of advertising technology, enabling them to maximize their revenue and sell their inventory smarter and safer."
Besides its headquarters in New York, the company also has offices in San Francisco, London, Berlin and Toronto. Admeld's 500 customers around the world include FOX News, Hearst Television, Discovery and The Weather Channel.
