Sina Weibo (Chinese: 新浪微博; pinyin: Xīnlàng Wēibó; literally "Sina Microblog") is a Chinese microblogging (weibo) website. Akin to a hybrid of Twitter and Facebook, it is one of the most popular sites in China, in use by well over 30% of Internet users, with a similar market penetration that Twitter has established in the USA. It was launched by SINA Corporation on 14 August 2009, and has more than 300 million registered users as of February 2012. About 100 million messages are posted each day on Sina Weibo.

"Weibo" (微博) is the Chinese word for "microblog(ging)". Sina Weibo launched its new domain name weibo.com on 7 April 2011, deactivating and redirecting from the old domain, t.sina.com.cn to the new one. Due to its popularity, the own published news of Sina.com and some other media use directly "Weibo" to refer to Sina Weibo sometimes. However, there are other China-based microblogging/weibo services including Tencent Weibo, Sohu Weibo and NetEase Weibo.

After the July 2009 Ürümqi riots, China shut down most of the domestic microblogging services including the first weibo service Fanfou. Many popular non China-based microblogging services like Twitter, Facebook and Plurk have been blocked from viewing since then. It was considered to be an opportunity to Sina's CEO Charles Chao. SINA Corporation launched the tested version of Sina Weibo on 14 August 2009. Basic functions including message, private message, comment and re-post were made possible in September, 2009. A Sina Weibo-compatible API platform for developing third-party applications was launched on 28 July 2010.