Tadatsune Shimazu (島津忠恒; November 27th 1576 - April 7th 1638) was a Daimyô pertaining to the Famille Shimazu and reigning on the Satsuma stronghold in the island of Kyūshū. It was one of most powerful the daimyô of its time. In 1603, the whole of its possessions represented 605.000 koku .

Tadatsune is the third wire of Yoshihiro Shimazu. To mark its honesty with Ieyasu Tokugawa, it changed its first name into Iehisa (家久).

Tadatsune, like his/her father and uncle was known for his bravery with the combat. And during the invasions of Hideyoshi Toyotomi in Korea, where it fought at the sides of his father, him and its army of 8000 men reflects in rout the army of Ming made up of 100.000 men.

It took the head of the family in 1602. In 1609 it adapted the Royaume of Ryūkyū what made it possible to the clan to grow rich thanks to the trade with the China. To support this trade, the clan did not completely annex this kingdom and left it semi-indépendant, indeed the Chinese would not have agreed to trade directly with Japanese.