Kōji Satō (佐藤 虹児 or 佐藤 虹ニ, Satō Kōji, 1 November 1911 – 30 May 1955) was a renowned Japanese amateur photographer, particularly in the 1930s.
From the age of thirteen Satō had a Thornton reflex camera; on his graduation from school he took photographs in his free time from his work in a bicycle wholesaler.
Satō's works were selected for the Golden Gate International Exposition in 1940.
After the war, Satō changed the characters for Kōji from 虹児 to 虹ニ.
An energetic and widely exhibited portraitist before and during the war, Satō turned his camera to his parents and his children after the war.