Flussio () is a comune (municipality) in the Province of Oristano in the Italian region Sardinia, located about northwest of Cagliari and about north of Oristano. As of 31 December 2004, it had a population of 492 and an area of .
Flussio borders the following municipalities: Magomadas, Modolo, Sagama, Scano di Montiferro, Sennariolo, Suni, Tinnura, Tresnuraghes.