Castelsardo Cathedral (Italian: Concattedrale di Sant'Antonio abate) is a cathedral in Castelsardo, northern Sardinia, Italy, and is dedicated to Saint Anthony the Great. It became the seat of the bishop of Ampurias in 1503. In 1839 the diocese of Ampurias was merged into that of Tempio, and the episcopal seat moved to Tempio Cathedral, when that of Castelsardo became a co-cathedral, as it remains in the present diocese of Tempio-Ampurias.