Monastir is a comune in the Province of South Sardinia in the Italian region of Sardinia, located about 20 kilometres northwest of Cagliari. As of 2011 census, it had a population of 4,505 inhabitants and an area of 31.8 square kilometres. Monastir borders the following municipalities: Nuraminis, San Sperate, Serdiana, Sestu, Ussana, Villasor.