Shimazu Tadatoki served as a bushō during the Sengoku and Azuchi-Momoyama periods.  Tadatoki was the seventh and last head of the Sasshū family, a cadet family of the Shimazu clan of Satsuma Province.

In 1565, Tadatoki was born as the lineal heir of Shimazu Yoshitora.

During the Pacification of Kyūshū by Toyotomi Hideyoshi, Tadatoki guarded Kōda to the south of Yatsushiro in the direction of Higo Province.  Owing to a betrayal of the Shimazu by Arima Harunobu of Shimabara in Hizen Province, Tadatoki withdrew to Izumi in the territory of the Shimazu clan.  In the fourth month of 1587, he surrendered to Toyotomi Hideyoshi and received official recognition of his rights to his territory.

In 1593, during the deployment to the Korean Peninsula for the Bunroku Campaign, Tadatoki served under Shimazu Yoshihiro but made a direct appeal to Hideyoshi to join a separate formation than Yoshihiro.  Hideyoshi dismissed the appeal from Tadatoki so he was forced to cross the Genkai Sea with Yoshihiro but, on the pretext of illness, did not make a landing in Korea.  Tadatoki’s actions infuriated Hideyoshi and, on 5/1 of Bunroku 2 (1593), he was turned over to the custody of Konishi Yukinaga at Uto Castle in Higo, incarcerated, and declared removed from his position.  His landholdings were then allocated to Hosokawa Yūsai and Ishida Mitsunari.  Before long, he died of illness at the Konishi camp on Gadeokdo Island in Korea.  He was twenty-eight years old.