The Roman Catholic Diocese of San Carlos de Ancud (in Latin: Dioecesis Sancti Caroli Anduciae) is a suffragan diocese of the archdiocese of Puerto Montt, in Chile.
It was established by Pope Gregory XVI, by means of the Bulla "Ubi Primum" on 1 July 1840.
The current Chilean dioceses of Villarrica, Valdivia, Osorno, Puerto Montt, Punta Arenas and the Apostolic Vicariate of Aysén have all been carved out of the original territory of the diocese of San Carlos de Ancud, at different times.
The diocese, which comprises the provinces of Chiloé and Palena, in the Los Lagos region of Chile, covers a territory of 24,283 km2 and has 26 parishes.
The diocesan cathedral ("El Sagrario" parish), is located in the city of Ancud.