Japanese regent, creator (in 880) of the post of kampaku, or chancellor, through which he acted as regent for four adult emperors until his death. This post allowed the Fujiwara family to dominate the Japanese government for more than three centuries.

Mototsune's uncle, and father through adoption, Yoshifusa, had acted as regent for the child emperor Seiwa, who ascended the throne in 858. Succeeding Yoshifusa as head of the Fujiwara family in 872, Mototsune assumed the post of regent when another minor, Yōzei, succeeded to the throne four years later. In order to further increase his power, Mototsune created the post of kampaku, which allowed him to exercise complete control over the government. When in 884 the emperor Yōzei challenged his rule, Mototsune forced his abdication. Subsequent heads of the Fujiwara family followed Mototsune in dominating Japan, but not all took the title kampaku.