Sina's Chinese-language Weibo product was launched about two years ago and claims more than 140 million users.
Technology blog TechWeb reported on Monday that Sina was going to launch an English microblog in the United States in a few months to rival Twitter.
Access to Twitter from within China is blocked by the Chinese government.

A worker walks past coal transportation facilities in Hami prefecture, Xinjiang Uygur autonomous region. China said it will increase imports of energy products, including coal, to help ease power shortage.
China will tackle an impending power shortfall by increasing energy imports, said the National Development and Reform Commission (NDRC), the top economic planner, on Wednesday.
The nation is expected to see a serious shortage this summer, said Li Yang, director-general of the NDRC's Bureau of Economic Operations Adjustment.
"With the coming of summer, the peak time for energy consumption, and the rapid growth of industrial production, the gap between electricity demand and supply will become more obvious and some areas may face a shortfall in coal and oil supplies," the bureau said in a statement.

The purchasing managers' index (PMI), a key gauge of manufacturing activity, hit a nine-month low in May, sparking fears that ongoing monetary tightening measures may slow economic growth.
But analysts said the economy would still manage a soft landing as the country tries to curb inflation and shift the economic growth pattern.
The PMI dropped to 52 in May, the China Federation of Logistics and Purchasing said on Wednesday.
The People’s Bank of China (PBOC) granted third party electronic payment licenses to 27 companies, reports Shenzhen Economic Daily, citing the central bank’s website.
The market had expected 32 companies to obtain the licenses.
Four Shenzhen-based companies, including Tenpay, the online payments provider of Tencent Holdings, were included in the list of 27 companies which obtained the licenses.

China's top automaker SAIC Motor Corp expects to top its full-year earnings forecast, banking on its diversified vehicle range, even as it projects overall growth in the country's vehicle sales to slow rapidly this year owing to inflation.
President Chen Hong said on Friday he expects the country's overall vehicle market to grow 7.4 percent this year to 19.7 million vehicles, slowing after an expansion in 2010 of nearly a third. SAIC is the Chinese partner of General Motors Co and Volkswagen AG.
"The environment of China's auto industry has turned from positive to neutral, and there are signs of an obvious slowdown," Chen told a shareholders' meeting.
"Inflationary pressure is relatively high, consumer confidence is weakening, the government has exited incentive policies, oil prices keep rising and Japan's earthquake has impacted the supply chain."
Read more: SAIC Motor upbeat amid slowing China vehicle sales
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