Riola Sardo, Arriora or Arriola in the Sardinian language, 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 2,132 and an area of .
Riola Sardo borders the following municipalities: Baratili San Pietro, Cabras, Narbolia, Nurachi, San Vero Milis.