Sina Corp, operator of China's most popular microblogging site, said it has bought 9.05 percent in China's second largest video site Tudou as it seeks to improve the attractiveness of its Weibo.com site to lure more users.

Sina paid US$66.4 million for the stake in Tudou, according to a filing to the United States Securities and Exchange Commission.

"Sina's investment is 'financial in nature' and both parties are open to future cooperation possibilities, but Tudou will retain its independence," an official with Tudou's financial department said yesterday.

Sina is adding video, social-networking and electronic commerce to its Weibo.com website, which boasted more than 200 million registered users by the end of June, to attract users in the world's biggest Internet market.

"Online videos are the easiest way to attract advertisers, so it's a good deal to invest in Tudou," said Hong Bo, an independent analyst.

Earlier this month Tudou raised US$174 million after selling its shares at US$29 each. By the end of the second quarter of this year the website took 14 percent of the domestic online video market but it still lagged arch rival Youku's 23 percent.

Market watchers suggested Sina's Weibo.com is able to draw a large number of visitors to Tudou.