During the Battle of Sekigahara in 1600, he had his nephew Masanari OTA join the Eastern (Tokugawa) army and his son Kazunari join the Western (Ishida) army, while he himself remained holed up in Uzuki-jo Castle, claiming illness.
1600年、関ヶ原の戦いでは甥の太田政成を東軍に、息子の一成を西軍に参加させ、自身は病と称して居城の臼杵城に立て籠もっていた。