John Kolosci (born November 26, 1974 in Portage, Indiana) is an American professional mixed martial artist. He was a fighter on Season 6 of The Ultimate Fighter , fighting on Team Serra.

Kolosci was able to defeat his 1st round opponent, Billy Miles, via Guillotine choke in the first round. In the second round, he fought Mac Danzig and was defeated by Rear naked choke in the first round, eliminating him from contention.

In the semifinal round, fighter Matt Arroyo suffered a rib injury and elected to pull out of the competition. In a meeting to decide his replacement, Kolosci was the only fighter to express enthusiasm at the prospect of fighting Danzig and was granted the opportunity by UFC president Dana White. In the rematch, Danzig was able to secure a victory, once again by Rear naked choke in round 1.

At The Ultimate Fighter Finale Kolosci lost to Matt Arroyo via armbar at 4:42 of the first round.