This was following a crackdown against online porn, dissident content, and prostitution by Chinese state media last month, who singled out WeChat as a particular offender.
And WeChat, which is owned by Tencent, have posted a statement on Weibo saying they have closed 20m accounts – roughly 5% of their total user base.
WeChat also said they shut 30,000 fake accounts.
Tencent have started offering rewards to users who report fraudulent or illicit accounts.
State media agency Xinhua said they would “hold service providers responsible if they do not fulfill their duty” following the crackdown, named Thunder Strike.
Last year, Tencent integrated payment tools for WeChat, where users link up their bank accounts and can purchase things or send money to each other.
Because of such payment tools, and a private messaging feature, the app has become widely used by sex workers.
Last year, a video went viral that showed prostitutes getting tutored on how to solicit customers on platforms like WeChat.
The app recently partnered with gift-giving startup Giftpass, to let users send presents that are redeemable with a QR-style code in-store.