Boris Grigoryevich Onishchenko (Russian and Ukrainian: ????? ??????????? ????????; also transliterated as Onyshchenko, Onishenko, Onischenko; born 19 September 1937) is a former Soviet modern pentathlete who competed at the 1968, 1972 and 1976 Summer Olympics.
He was a multiple Olympic and world champion, but was disqualified for cheating at the 1976 Summer Olympics and banned for life from sports.