Casalpusterlengo is a comune (municipality) in the Province of Lodi in the Italian region Lombardy, located about 50 kilometres (31 mi) southeast of Milan and about 20 kilometres (12 mi) southeast of Lodi.

It received the honorary title of city with a presidential decree on October 30, 1975. Sights include the church of Sts. Bartholomew and Martin (14th century), the communal palace and a tower from the medieval castle. A bedroom where Napoleon Bonaparte slept is preserved in via Cavour.