The Diocese of Viana do Castelo (Latin: Dioecesis Vianensis Castelli), is a Latin Church diocese of the Catholic Church in the Norte Region of Portugal.

It has existed since 1977.

It is a suffragan of the archdiocese of Braga, with its see at Viana do Castelo.

[1] The current bishop is João Evangelista Pimentel Lavrador.

[2]