The company, which publishes magazine titles including Property Week and Building magazine in the UK, will pay an initial $1m (£642,325) for the agency which specialises in banner ads for the online video game industry.
A further performance-related payment of up to $7m (£4.50) will also be paid.
UBM said Game Advertising Online, which it purchased from private owners, was expected to generate revenue of approximately $4m in the twelve months to March, 2010.
The new acquisition, which marks a move away from traditional print publishing, will be run through UBM's business technology wing, TechWeb.
Tony Uphoff, chief executive officer of TechWeb, said: "GAO provides us with both revenue growth potential and a new business model that will serve us well as we look to expand our business with online game publishers and with consumer-oriented online game websites."
Earlier this year, UBM closed its 15 year-old UK bar and restaurant sector title, Theme magazine.
The closure came after UBM predicted last summer that it would be forced to shut titles as the magazine world was "significantly over published".
The company, which also has substantial and growing events and information businesses, revealed in August that it closed 15 print titles in the first half of last year.
During that same period UBM's operating profit was down 11.3 per cent to £78.3m on revenue down 2.4 per cent to £435m - operating profit from print magazines dropped 77.9 per cent in the first half to £3.3m.