Masaaki Koyama (?? ??, Koyama Masaaki, born July 28, 1934 in Akashi, Hyogo Prefecture, Japan) is a Japanese former professional baseball pitcher in Nippon Professional Baseball (NPB).
He played for the Osaka / Hanshin Tigers from 1953 to 1963, the Tokyo / Lotte Orions from 1964 to 1972, and the Taiyo Whales in 1973.
He is a member of the Japanese Baseball Hall of Fame.
A right-handed pitcher, Koyama threw hard and was known for his effective slider and pinpoint control.
He ranks third all-time in the NPB in wins (320), strikeouts (3,159), innings pitched (4,899), and shutouts (74).
He won 20 or more games 7 separate times, was selected to eleven All-Star teams, and won the 1962 Eiji Sawamura Award.