A release from the school on Friday said Holmes did not meet Horn's expectations both on and off the court, but didn't specify what the junior did to get kicked off the team.
Holmes hasn't played since Nov. 27 after he broke a bone near his left eye at home.
Holmes was averaging 11 points and 4.8 rebounds a game this season, after scoring 10.8 points and a team-best 7.7 rebounds in 2008-09.
Horn says he will help Holmes continue his education and basketball career.
Holmes is the second starter the Gamecocks have lost this season. Senior Dominique Archie suffered a season-ending knee injury on Nov. 22.