San Giulio Island or St. Julius Island (Italian: Isola di San Giulio) is the only island within Lake Orta in Piedmont , northwestern Italy. The most famous building on the island is the Basilica di San Giulio close to which is the monumental old seminary (1840s). Since 1976 it has been transformed into a Benedictine monastery.

The island is 275 m (902 ft) long (north/south) and is 140 m (459 ft) wide (east/west). The little island, just west of the lakeshore village of Orta San Giulio , has very picturesque buildings and takes its name from a local patron saint (Julius of Novara ), who lived in the second half of the 4th century.