Caiolo () is a (municipality) in the Province of Sondrio in the Italian region of Lombardy, located about northeast of Milan and about southwest of Sondrio. As of 31 December 2004, it had a population of 994 and an area of .
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.