The 68-year old US actor signed autographs for fans on Saturday at the modern art museum in Nice, where his "Real Love" exposition is running for two weeks.
"Painting, without a doubt, is the most honest form of all the arts. Because it's simple, unforgiving, and it's there to be studied up-close and personal. And you can't defend it, it's there. So I think it's the most honest of all the arts," Stallone, sitting alongside Nice Mayor Christian Estrosi, told a press conference.
Stallone, an Academy-award nominated actor as well as a director and screenwriter, studied art before his film career took off, and has also had shows in Russia, Switzerland and Miami.
Estrosi praised Stallone's work on Twitter. "The exposition 'Real Love' ... reveals an inspired painter, a side often overlooked," wrote the mayor.