Masamitsu was the son of Yukimasa OTA, a Zaichokanjin (the local officials in Heian and Kamakura periods) of Musashi Province who was believed to be descended in a direct line from FUJIWARA no Hidesato.
武蔵国の在庁官人で藤原秀郷の直系子孫とされる太田行政の子。