The 2004–05 Serie C1 was the twenty-seventh edition of Serie C1, the third highest league in the Italian football league system.
It was contested by 19 teams, and U.S. Cremonese won the championship. It was decided that U.S. Cremonese, A.C. Mantova was promoted to Serie B, and A.S. Andria BAT, F.C. Vittoria, Calcio Como, A.C. Prato was demoted in Serie C2.
It was contested by 18 teams, and Rimini Calcio F.C. won the championship. It was decided that Rimini Calcio F.C., U.S. Avellino was promoted to Serie B, and A.C. Reggiana 1919, Benevento Calcio, SPAL 1907, A.S. Sora, A.S.D. Nuova Vis Pesaro Calcio 2006 was demoted to Serie C2.