| Sun Jiajun | |
| Nationality: | Chinese |
| Birth Date: | 1 August 2000 |
| Birth Place: | Yichang, Hubei, China |
| Height: | 1.83 m [1] |
| Weight: | 75 kg |
| Strokes: | Breaststroke, Butterfly stroke |
| Show-Medals: | yes |
Sun Jiajun (born 1 August 2000) is a Chinese swimmer.[2] He won the gold medal in the boys' 100-metre breaststroke and 4 × 100-metre mixed medley relay events at the 2018 Summer Youth Olympics held in Buenos Aires, Argentina. He also won the silver medal in the boys' 50-metre breaststroke and 4 × 100-metre medley relay categories in the same event.[3] [4] In 2021, he qualified to represent China in the men's 4 × 100-metre medley relay event at the 2020 Summer Olympics held in Tokyo, Japan.[2]