Comacchio Cathedral (Italian: Duomo di Comacchio; Cattedrale di San Cassiano), also the Basilica of San Cassiano, is a Baroque Roman Catholic cathedral and minor basilica dedicated to Saint Cassian of Imola (San Cassiano) in the city of Comacchio, in the province of Ferrara, Emilia-Romagna, Italy.

Dedicated to the patron of the town, this church stands on the site of the ancient Romanesque cathedral built in 708 and torn down in 1694.

Construction of the new cathedral began in 1659 under the Bishop of Comacchio, Sigismondo Isei, with consecration finally in 1740.

The apse houses the 18th-century marble altar and the 16th-century wooden statue of the Martyr Cassiano, patron of the town and diocese.

Above the entry portal is the organ, built in 1728 in Modena by Giovanni Domenico Traeri.