The move by users who call themselves "TikTok refugees" has made RedNote the most downloaded app on Apple's US App Store on Monday.
It has about 300 million monthly users and looks like a combination of TikTok and Instagram. It allows users, mostly young urban women, to exchange lifestyle tips from dating to fashion.
Supreme Court justices are due to rule on a law that set a 19 January deadline for TikTok to either sell its US operations or face a ban in the country.
TikTok has repeatedly said that it will not sell its US business and its lawyers have warned that a ban will violate free speech protections for the platform's 170 million users in the US.
Meanwhile, RedNote has welcomed its new users with open arms. There are 63,000 posts on the topic "TikTok refugee", where new users are taught how to navigate the app and how to use basic Chinese phrases.
As more US users joined RedNote, some Chinese users have also jokingly referred to themselves as "Chinese spies", a reference to US officials' concerns that TikTok could be used by China as a tool for spying and political manipulation.