The 50-year-old attracted almost five million followers in 12 hours after posting a selfie with Lisa Kudrow, Courteney Cox, Matt LeBlanc, David Schwimmer and Matthew Perry.
The post followed her recent revelation that the cast had met up at Cox's home.
"And now we're Instagram FRIENDS too. HI INSTAGRAM," the actress wrote.
After her profile appeared not to accept new followers for a short time because of a technical difficulty, Aniston joked: "Sorry, I think I broke it."