Guamaggiore is a comune (municipality) located in the Metropolitan City of Cagliari within the Italian region of Sardinia. It is situated approximately 40 kilometres (25 mi) north of the regional capital, Cagliari.
The municipality borders the towns of Gesico, Guasila, Ortacesus, and Selegas. A notable historical landmark in Guamaggiore is the Gothic church of St. Peter, which dates back to the 13th-14th century.