Juraj Ontko (born 23 December 1964 in Liptovský Mikuláš) is a Czechoslovak-Slovak slalom canoeist who competed at the international level from 1981 to 1998.
He won five medals at the ICF Canoe Slalom World Championships.
A silver and a bronze for Czechoslovakia in the C1 team event (1983, 1987) and a gold (C1 team: 1997) and two bonzes for Slovakia (C1 team: 1995, C2 team: 1993).
He also won a gold medal in the C1 team event at the 1998 European Championships.Ontko competed for Czechoslovakia at the 1992 Summer Olympics in Barcelona, finishing eighth in the C1 event.
His partner in the C2 boat was Ladislav Cáni.