San Nazzaro Sesia is a comune (municipality) in the Province of Novara in the Italian region Piedmont, located about 70 kilometres (43 mi) northeast of Turin and about 15 kilometres (9 mi) west of Novara.

San Nazzaro Sesia borders the following municipalities: Albano Vercellese, Biandrate, Casalbeltrame, Casalvolone, Greggio, Oldenico, Recetto, and Villata. It is home to the Abbey of San Nazzaro e Celso, one of the most important Romanesque complexes in Piedmont.

The abbey is one of the most significant monastic complexes in Piedmont. It consists of a surrounding wall with circular corner towers, a tall Romanesque bell tower, a church in Lombard Gothic style, and an elegant cloister featuring a 15th-century cycle of frescoes depicting the stories of Saint Benedict.

The Sanctuary, dating back to the 16th century, is located about 1.5 km from the town center, at the end of a long tree-lined avenue.