Caiolo (Lombard: Cajoeul) 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 5 kilometres (3 mi) southwest of Sondrio. As of 31 December 2004, it had a population of 994 and an area of 33.3 square kilometres (12.9 sq mi).

Caiolo borders the following municipalities: Albosaggia, Carona, Castione Andevenno, Cedrasco, Foppolo, Piateda, Postalesio, Sondrio.

The church of San Vittore has Renaissance frescoes by Vincenzo De Barberis.