Tréguier Cathedral (French: Cathédrale Saint-Tugdual de Tréguier) is a Roman Catholic church and former cathedral in Tréguier, Côtes-d'Armor, France. It is dedicated to Saint Tudwal. The church was formerly the seat of the Bishopric of Tréguier, abolished under the Concordat of 1801, when its territories were divided between the Diocese of Quimper and the Diocese of Saint-Brieuc, known since 1852 as Saint-Brieuc-Tréguier.