Men Behind the Sun (Chinese: 黑太陽731, literally Black Sun: 731, also sometimes called Man Behind the Sun) is a 1988 Hong Kong historical exploitation horror film directed by T. F. Mou, and written by Mei Liu, Wen Yuan Mou and Dun Jing Teng. The film is a graphic depiction of the war atrocities committed by the Imperial Japanese Army at Unit 731, the secret biological weapons experimentation unit of the Imperial Japanese Army during the Second Sino-Japanese War. It details the various cruel medical experiments Unit 731 conducted on Chinese and ethnic Russian prisoners towards the end of the war.

It is the first film to be classified "level III" (equivalent to the US rating NC-17) in Hong Kong.