Sengaku (year of birth and death unknown) was a Buddhist monk during the late Heian period. He was from the Kajuji line of the Northern House of the Fujiwara clan and he was a son of FUJIWARA no Morizane who held the position of Tosa no kami (Governor of Tosa Province). His siblings included FUJIWARA no Akinori, and the wife of FUJIWARA no Tadazane (the mother of FUJIWARA no Yorinaga).
He entered the Kofuku-ji Temple to study under Ryukaku Sojo (high-ranking Buddhist priest), and was granted the rank of Gon no Risshi (a provisional rank in the lowest managerial position) in 1153. Three years later, in 1156, he joined his nephew FUJIWARA no Yorinaga and fought for Retired Emperor Sutoku during the Hogen War. Because Yorinaga, defeated and injured in the War, died in Sengaku's cell at the Kofuku-ji Temple, and Sengaku patronized Tadazane, who was the father of Yorinaga and had fled from Nanto (southern capital - Nara), along with Nobuzane and Jinpan, his land was confiscated under the charge of deep involvement in the War.