Born in Komoro, Nagano Prefecture. He graduated from Ueda Middle School and left Keio University. At the Kawabata Painting School he studied under Takeji Fujishima. After travelling to America on the recommendation of Toson Shimazaki, he learned the grounding of oil painting from Charles Guérin. In 1972 he gave his works to Komoro, the city of his birth, and founded the Keizo Koyama Art Foundation; in 1975 the Komoro Municipal Keizo Koyama Museum of Art opened. Director of the Nitten. Person of Cultural Merit. Recipient of the Order of Culture.