The Basilica di San Giulio is a Roman Catholic church on the small San Giulio Island in the center of Lake Orta , Province of Novara , north-western Italy. It has the status of a minor basilica. Although the island is part of the Orta San Giulio municipality, the basilica belongs to the San Giacomo parish, including the island and a portion of the west coast of the lake in San Maurizio d'Opaglio municipality.

According to tradition, it was the hundredth, and last, church founded by Julius of Novara and his brother Julian, both natives of Aegina in Greece, who dedicated their later years to the evangelization of the area around Lake Orta. Legend has it that around year 390 the saint reached the island sailing on his cloak, and then freed it from dragons (symbols of paganism); after the defeat of the monsters he built a small church devoted to the Twelve Apostles.

In the Early Middle Ages, the strategic position made the island an important defensive point; first, it was the abode of a Lombard duke, then Berengar II of Italy built a castle there.