Ryo Chonan (born October 8, 1976 in Tsuruoka, Yamagata, Japan) is a Japanese mixed martial artist, currently competing for the Ultimate Fighting Championship. He has previously competed in PRIDE Fighting Championships and DEEP.

One of Chonan's wins was against future UFC middleweight champion Anderson Silva at PRIDE: Shockwave 2004, where he executed a flying scissor-lock takedown, followed quickly by a heel-hook submission. In the 2005 PRIDE Welterweight Grand Prix, Chonan suffered a broken orbital bone at the end of his match against Joey Villasenor caused by a stomp but was able to continue in the tournament. In his next match of the tournament, against Paulo Filho, Chonan was submitted by armbar early in the first round.

In February 2007, Chonan returned to DEEP and defeated former DEEP middleweight champion Ryuta Sakurai to retain the middleweight championship.

Ryo Chonan made his UFC debut against Karo Parisyan on November 17, 2007 at UFC 78 which Chonan lost via unanimous decision after three rounds.

Chonan then defeated Roan Carneiro via split decision on September 6, 2008 at UFC 88.

Chonan was also defeated in his next fight on December 27, 2008 by Brad Blackburn.

Chonan is currently a part of the Team Quest, along with former PRIDE Fighting Championships middleweight and welterweight champion Dan Henderson, Matt Lindland, Jason Miller "Mayhem", and Rameau Thierry Sokoudjou.