Chinese internet company Sina Corp.’s quarterly profit surged in the most recent period, driven by more than $100 million in investment gains and continued strength at microblog portal Weibo Corp.

An internet pioneer in China, Shangai-based Sina was founded in 1999 from the merger of Stone Rich Sight Information Technology Co., a Beijing software company, and Sinanet.com, a California-based company that ran internet sites targeted at Chinese abroad. Sina spun out Weibo in 2014 but kept a controlling stake, which last month...