Maillezais Cathedral (Cathédrale Saint-Pierre de Maillezais) is a ruined Roman Catholic cathedral in the commune of Maillezais in the Vendée, France. Formerly the Abbey of Saint-Pierre, the ruins consist of a church, refectory, dormitory, kitchen, cellars, turrets and ramparts. The cathedral has been declared as a heritage monument in reflection of its Romanesque, Gothic and Renaissance form. It was designated as a monument historique on 30 January 1924. The cathedral belonged to the Diocese of Luçon with rites of Roman (Latin) with St. Peter as the Patron Saint.