Google's contracts with large Chinese advertising resellers will end on 27 October, the company has announced.
In September Google said it would end the contracts, but has not given a reason for the decision.
It is thought the move will benefit China's leading search engine Baidu, which has more than 70% of the country's search market revenue.
This follows figures from research firm Analysys which found that Google's share of China's online market fell to 24.2% in the three months to June, from 30.9% in the first quarter.
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China renewed Google's licence in July, after the web giant threatened to close its operations because of concerns about state censorship
The renewal came after the firm set up a new landing page at google.cn with links to its uncensored Hong Kong search engine.