Kiyoshi Oka (岡 潔, Oka Kiyoshi, April 19, 1901 – March 1, 1978) was a Japanese mathematician who did fundamental work in the theory of several complex variables.

He went to Kyoto Imperial University in 1919, turning to mathematics in 1923 and graduating in 1924.

He published solutions to the first and second Cousin problems, and work on domains of holomorphy, in the period 1936–1940.

He received his Doctor of Science degree from Kyoto Imperial University in 1940.

These were later taken up by Henri Cartan and his school, playing a basic role in the development of sheaf theory.