Tadao Tannaka (淡中 忠郎 Tannaka Tadao?, December 27, 1908 – October 25, 1986) was a Japanese mathematician. He is best known for developing the theory of Tannaka–Krein duality, which generalizes Pontryagin duality to noncommutative compact groups.
Tannaka was born in Matsuyama, Ehime Prefecture. After receiving a Bachelor of Science in mathematics from Tohoku Imperial University, he was appointed a lecturer in the university in 1934 and was promoted to a full professor in 1945. He died in Tokyo.