 Ōishi later joined the "Rikken Kokumintō" and was at one point a contender against Inukai Tsuyoshi for its leadership.In 1913, he broke with Inukai, and joined Katsura Tarō’s new Rikken Dōshikai, where he was ranked as one of its five leaders.He retired from politics in 1915, after having been elected to the Lower House of the Diet of Japan for six terms.