The partnership with Gridsum will give iCrossing access to in-country search capabilities in Asia, where the search market is expected to grow by $1.9bn (£1.3bn) by 2011, according to iResearch.
ICrossing currently manages paid and natural search marketing campaigns in 21 languages in more than 25 countries across the Americas, EMEA and Asia Pacific.
Gridsum provides search engine marketing and analytics to China's emerging online market. It was founded in 2003 by a group of professionals from Tsinghua University, Peking University and Silicon Valley.
Michael Yang Xu, senior vice president of Gridsum, said: "ICrossing has a worldwide reputation for their search leadership and innovation.
"Their strong international presence, experience working with global brands and unique approach to search-informed digital marketing make them a perfect partner."
Jeffrey Pruitt, executive vice president of corporate partnerships at iCrossing, said: "We were impressed with Gridsum's technical capabilities and understanding of the market.
"This partnership will help increase our presence and global offering in one of the fastest growing search markets in the world."