Shimazu Tadahisa (島津 忠久, died August 1, 1227) was the founder of the Shimazu samurai clan.
According to a record of his life, he was reportedly born in Sumiyoshi Taisha in Osaka. He was initially Koremune Tadayoshi (惟宗忠久) but after being given the territory of Shimazu, Hyūga Province to rule from by Minamoto no Yoritomo, he took the name of Shimazu.
Tadahisa was a son of the Shogun Minamoto no Yoritomo (1147–1199) by the sister of Hiki Yoshikazu.
He married a daughter of Koremune Hironobu, descendant of the Hata clan, whose name Tadahisa at first took.
He received the domain of Shioda (Shinano province) in 1186 and was then named Shugo of Satsuma province. He sent Honda Sadachika to take possession of the province in his name and accompanied Yoritomo in his expedition to Mutsu in 1189. He went to Satsuma in 1196, subdued Hyūga and Ōsumi provinces, and built a castle in the domain of Shimazu (Hyūga) which name he also adopted. He is buried in Kamakura, near his father's tomb.