Gratianopolis was an ancient city and Roman Catholic diocese in Mauretania Caesariensis in present-day Algeria. It was one of several towns named after the Roman emperor Gratian (367 to 383), and is only known from mentions in church council minutes. Its history, location and present condition are unknown. The name survives as a Roman Catholic titular see, and since 1911 has been the title of the Greek Catholic Apostolic Exarchate.