| Birth Date: | 26 March 1877 |
| Birth Place: | Ivanteyevka, Moscow Oblast, Russian Empire |
| Death Place: | Brussels, Belgium |
Oscar Grégoire Jr. (26 March 1877 – 28 September 1947) was a Belgian water polo player and backstroke swimmer who competed in the 1900 Summer Olympics, in the 1908 Summer Olympics, and in the 1912 Summer Olympics.[1] He was part of the Belgian water polo team and was able to win two silver and one bronze medal. In 1908 and 1912 he also participated in the 100-metre backstroke events, but was eliminated in the first round in both.