Sadao Watanabe (渡辺 貞夫, Watanabe Sadao, born February 1, 1933) is a Japanese jazz musician who plays alto saxophone, sopranino saxophone, and flute. He is known for his bossa nova recordings, although his work encompasses many styles, with collaborations from musicians all over the world.

Born in Utsunomiya, Japan, Sadao first began learning music at the age of 18 and started performing professionally in 1953. By 1958 he had performed with leading musicians and quartets. In 1962 he left Japan to study at Berklee College of Music in Boston. He has had more than 10 albums reach the top 50 Billboard charts and two within the top 10. He has also had numerous albums reach number one on the jazz charts.

On July 22, 1966, he played with the John Coltrane quintet in Tokyo while the group was touring Japan.