Ogasawara Nagakuni (小笠原 長国, July 9, 1824 – April 23, 1877) was the 6th and final daimyō of Karatsu Domain in Hizen Province, Kyūshū, Japan (modern-day Saga Prefecture). Before the Meiji Restoration, his courtesy titles were title of Sado no Kami and junior 5th, lower grade court rank (ju go i no ge 従五位下).