Ōuchi clan (大内氏, Ōuchi-shi) was one of the most powerful and important families in Western Japan during the reign of the Ashikaga shogunate in the 12th to 14th centuries. Their domains, ruled from the castle town of Yamaguchi, comprised six provinces at their height, and the Ōuchi played a major role in supporting the Ashikaga in the Nanboku-cho Wars against the Imperial Court. The Ōuchi remained powerful up until the 1560s, when they were eclipsed by their vassals, the Mōri clan.