Castelmauro is a comune (municipality) in the Province of Campobasso in the Italian region Molise, located about 30 kilometres (19 mi) north of Campobasso. As of 31 December 2004, it had a population of 1,825 and an area of 43.5 square kilometres (16.8 sq mi).
Castelmauro borders the following municipalities: Acquaviva Collecroce, Civitacampomarano, Guardialfiera, Montefalcone nel Sannio, Roccavivara, San Felice del Molise, Trivento.