Castiadas is a comune (municipality) in the Province of Cagliari in the Italian region Sardinia, located about 35 km east of Cagliari. As of 31 December 2004, it had a population of 1,343 and an area of 102.3 km².
Castiadas borders the following municipalities: Maracalagonis, Muravera, San Vito, Sinnai, Villasimius.