Oulu Castle (Swedish: Uleåborgs slott, Finnish: Oulun linna) was a late defense castle in Oulu, Finland. It was built on an island in the delta of Oulu River in 1590. The castle was mostly made of wood and earth walls. There probably was an earlier medieval castle on the same site latest by 1375. The Russian has recorded that men from Novgorod tried to conquer a new castle in the Oulu River delta in 1377 but were unsuccessful.