Gainer is a surname. Notable people with the name include:
Aaron Gainer, member of American Christian post-grunge band '12 Stones'
Alice Gainer (born 1982), American television reporter
Del Gainer (1886–1947), American baseball player
Derrick Gainer (American football) (born 1966), American football player
Derrick Gainer (born 1972), American boxer
Sir Donald Gainer (1891–1966), British ambassador
Elmer Gainer (1918–1970), American basketball player
Forrest Gainer (born 1979), Canadian rugby player
Frank Gainer (1888–1975), Canadian politician
Glen Gainer, Jr. (1927–2009), American politician
Glen Gainer III (born 1960), American politician
Jay Gainer (born 1966), American baseball player
John L. Gainer (born 1938), American chemical engineer
Ronald William Gainer (born 1947), American Catholic priest, appointed Bishop of Harrisburg in 2014
Steve Gainer, American cinematographer
Terrance W. Gainer (born 1947), Sergeant at Arms of the United States Senate 2007–14
