Kimotsuki Kaneoki served as a bushō during the Sengoku period.  He was the fifteenth head of the Kimotsuki clan and served as the lord of Kōyama Castle in Ōsumi Province.  He had the common name of Matahachirō.

In 1492, Kaneoki was born as the son of Kimotsuki Kanehisa, the fourteenth head of the Kimotsuki clan.  In 1523, after the death of his father, Kanehisa, Kaneoki inherited the headship of the clan.

Kaneoki established through political marriages an alliance with the Shimazu clan of Satsuma Province but, in 1524, Kaneoki recaptured Kushira Castle (which had been the base of the Kitahara clan in Ōsumi) from a father-in-law named Shimazu Tadatomo of the Hōshū, a cadet family of the Shimazu.  Thereafter, he moved his base to Kōyama Castle and, amidst ongoing disputes with the Shimazu clan, endeavored to expand his base of power.

In 1533, Kaneoki died at the age of forty-two.  After his death, a succession struggle erupted between his son, Kimotsuki Kanetsugu, and Kaneoki’s younger brother (Kimotsuki Kanechika).  Kanetsugu prevailed and became the successor.