Sei Koyanagui was born in 1896, and was a Japanese painter during the first half of the 20th century.

At first Koyanagui studied in Tokyo. He later went to Paris around 1920, where he met many different painters. There he made contact with the artists group headed by his fellow-countryman Tsuguharu Foujita.

The artist mainly painted animals and flowers, as well as female nudes, which form an important part of his work.