Postalesio (Lombard: Pustalés) is a comune (municipality) in the Province of Sondrio in the Italian region of Lombardy, located about 90 kilometres (56 mi) northeast of Milan and about 6 kilometres (4 mi) west of Sondrio. As of 31 December 2004, it had a population of 618 and an area of 10.6 square kilometres (4.1 mi²).

Postalesio borders the following municipalities: Berbenno di Valtellina, Caiolo, Castione Andevenno, Cedrasco, Fusine, Torre di Santa Maria.