The 2003–04 Illinois Fighting Illini men's basketball team represented 98th season University of Illinois at Urbana-Champaign in the 2003-04 NCAA Division I men's basketball season.

Weber arrived in Champaign after directing the Southern Illinois Salukis for five seasons.

Weber’s inaugural season directing the Orange and Blue was a success, as he became just the third coach in Big Ten history to win an outright conference championship in his first season.

Weber also guided Illinois to its first NCAA Tournament victory over a higher seeded team, when the No.

The Illini finished the year with a record of 26-7 and advanced to the NCAA Sweet Sixteen.