Postalesio () is a (municipality) in the Province of Sondrio in the Italian region of Lombardy, located about northeast of Milan and about west of Sondrio. As of 31 December 2004, it had a population of 618 and an area of .
Postalesio borders the following municipalities: Berbenno di Valtellina, Caiolo, Castione Andevenno, Cedrasco, Fusine, Torre di Santa Maria.