Sini is a comune (municipality) in the Province of Oristano in the Italian region Sardinia, located about 60 kilometres (37 mi) northwest of Cagliari and about 30 kilometres (19 mi) southeast of Oristano. As of July 2021, it had a population of 545 and an area of 8.7 square kilometres (3.4 mi²) in December 2004.

Sini borders the following municipalities: Baradili, Genoni, Genuri, and Gonnosnò.