The Co-Cathedral of Saint Julian (Galician: Concatedral de San Xiao; Spanish: Catedral de San Julian) is a Roman Catholic co-cathedral in the town of Ferrol in the autonomous community of Galicia, Spain.

The church was erected in the 18th-century, designed by Julián Sánchez Bort, who based his Neoclassical design on the church of Sant'Andrea delle Fratte in Rome.

The church was made co-cathedral along with the Cathedral of Mondoñedo in 1959.

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