Siddi is a comune (municipality) in the Province of South Sardinia in the Italian region Sardinia, located about 50 km northwest of Cagliari and about 11 km north of Sanluri in the Marmilla historical sub-region. Siddi borders the following municipalities: Baressa, Collinas, Gonnoscodina, Gonnostramatza, Lunamatrona, Pauli Arbarei, Ussaramanna. It is home to several archaeological findings, including a domus de janas from the Ozieri culture, a Giants' tomb and several nuraghe villages.