Postalesio is a [[comune]] (municipality) in the Province of Sondrio in the Italian region of Lombardy, located about 90 km northeast of Milan and about 6 km west of Sondrio. As of 31 December 2004, it had a population of 618 and an area of 10.6 km2.

Postalesio borders the following municipalities: Berbenno di Valtellina,