The Man Down singer passed Gaga on the social networking website yesterday - and has managed to get around 20,000 more followers than the 25-year-old.
Figures show this morning that Rihanna, 23, has 40,564,905 Facebook fans compared to the Born This Way hitmaker's 40,543,536.
It shows a big rise in Rhi Rhi's online popularity, but Gaga still has more followers than her on Twitter.
Gaga, real name Stefani Germanotta, remains top of Twitter with 11.6 million followers, followed by teen pop star Justin Bieber on 11 million.