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 in the western tip of Honshu island, comprised six provinces at their height, and the Ōuchi played a major role in supporting the Ashikaga in the Nanboku-cho Wars against the Southern Imperial Court.

Local legend in modern Yamaguchi City has it that the Ōuchi clan were of Korean origins, specifically descended from a prince of Baekje.

The Ōuchi-shi Jitsruroku (大内氏実録),[1] a work of the historian Kondō Kiyoshi (近藤清石, 1833–1916), is one of the books which adopt this legend.

[5] Based in Suō Province, towards the western end of Honshū, the Ōuchi were among the primary families to be involved in foreign trade and relations, particularly with Ming China.