| Intro | South African sprinter |
| A.K.A. | Justus Kinloch Ayres Oosterlaak |
| Was | Athlete |
| From | South Africa |
| Type | Sports |
| Gender | male |
| Birth |
15 January 1896, Wellington, South Africa |
| Death |
5 June 1968, Pretoria, South Africa |
| Star sign | Capricorn |
Jack Oosterlaak (Justus Kinloch Ayres Oosterlaak; 15 January 1896, in Wellington – 5 June 1968), was a South African athlete who competed mainly in the 400 metres.
He competed for South Africa in the 1920 Summer Olympics held in Antwerp, Belgium in the 4 x 400 metre relay where he won the Silver medal with his teammates Harry Davel, Clarence Oldfield and Bevil Rudd.