Yao Gang, vice chairman of the China Securities Regulatory Commission (CSRC), who first came under suspicion of "severe disciplinary violations" in November, was "dismissed" from his post, China's state council, or the cabinet, said in a statement on its website.
Disciplinary violation normally refers to graft.
Chinese authorities have launched a series of investigations into the financial sector after a debt-fuelled stock market bubble -- encouraged by authorities -- burst in the summer in a rout that wiped out trillions of dollars in market capitalisation.
Several securities firms and executives have also come under suspicion.
After conducting internal graft investigations, the Communist Party can punish alleged offenders internally or expel them and pass them onto courts for trial, where conviction is virtually guaranteed.