Yahoo Japan has said that it will adopt Google's search engine technology, rather than Microsoft's which is used by its strategic partner Yahoo Inc.
The company said the deal would not affect the position of Yahoo Inc as its strategic partner.
Yahoo Japan is 35%-owned by Yahoo Inc, but its majority shareholder is mobile phone and internet service provider Softbank, which has a 40% stake.
Yahoo Japan is the most popular search engine website in Japan.
It has about a 57% share of the market, while Google's share is just over 30%. Microsoft has a share of about 3%.
The deal will see Yahoo Japan use online advertising and distributions systems developed by Google.
The announcement was made alongside Yahoo Japan's first-quarter results.
The company reported a net profit of 21.7bn yen ($248m; £160m) for the three months to June, up 13% from the 19.2bn yen it made in the same period a year ago.