Softbank is Yahoo Japan's biggest shareholder with a 40 percent stake and also owns a 29 percent stake in Alibaba, making it the Chinese company's second biggest shareholder. Alibaba's Ma sits on Softbank's board.
Alibaba.com, the company's unit that operates a Website where businesses buy and sell goods to each other, was listed on the Hong Kong Stock Exchange in November last year.
The stock has fallen 62 percent this year, compared with an 18 percent drop for the benchmark Hang Seng Index. Yahoo's shares have lost 15 percent.
The Chinese company also owns closely held Taobao.com, which lets individuals post items for sale.
Taobao.com users sold 43.3 billion yuan (US$6.33 billion) of merchandise last year.
(Shanghai Daily August 4, 2008)