Kaji Hidetsuna served as a bushō during the Sengoku period. He was a retainer of the Uesugi clan.
The Kaji were members of the Sasaki clan in the Agakita Group.
Hidetsuna was born as the son of Kaji Harutsuna and the older sister of Uesugi Kenshin. As a family member, Hidetsuna served Kenshin and made significant contributions at the Battle of Kawanakajima. When the death of Kenshin gave rise to a succession struggle known as the Otate Conflict, Hidetsuna aligned with Uesugi Kagetora (the natural son of Hōjō Ujiyasu adopted by Uesugi Kenshin) against Uesugi Kagekatsu (Hidetsuna’s cousin).
After a surprise assault by supporters of Uesugi Kagekatsu on Kaji Castle, the base of Ijimino Harunaga (later known as Shibata Shigeie) and Ijimino Nobumune, Hidetsuna surrendered at once.
In 1581, Hidetsuna supported a rebellion by Shigeie and continued to resist Kagekatsu. In advance of an attack on Shibata Castle, on 9/7 of Tenshō 15 (1587), Kagekatsu toppled Kaji Castle during which Hidetsuna was killed in action.