Yang Weidong was with Youku for five years, before Alibaba acquired the company in 2015.
An Alibaba spokeswoman says Yang "is understood to be assisting Mainland authorities with an investigation into an alleged case of seeking economic benefits.”
Alibaba didn't detail Yang's connect to the probe or say when he left the company.
Alibaba Pictures head Fan Luyuan has stepped into the vacant role.
Alibaba shares are up 0.6% premarket to $164.70.
Subscribe for full text news in your inbox