Katsuma Dan (團 勝磨, Dan Katsuma, October 16, 1904 – May 18, 1996) was a Japanese embryologist and cell biologist. He was born in 1904 in Tokyo, the youngest son of Baron Dan Takuma, president of the Mitsui Gomei Kaisha Corporation. Takuma Dan was educated in the United States, graduating from MIT in 1878. He was one of the first foreign students to be educated at MIT and later, as president of the Japan Steel Works, he initiated and maintained close research ties with The Institute. Katsuma Dan died in 1996 in Osaka, Japan, at the age of 91.