Oleggio is a comune (municipality) in the Province of Novara in the Italian region Piedmont, located about northeast of Turin and about north of Novara. As of 31 December 2004, it had a population of 12,490 and an area of .
Among its churches is the 10th-century, Romanesque-style San Michele.
Oleggio borders the following municipalities: Bellinzago Novarese, Marano Ticino, Mezzomerico, Momo, Vaprio d'Agogna, and Vizzola Ticino.