| Kei Marumo | |
| Strokes: | Synchronized swimming |
| Birth Date: | 6 March 1992 |
| Birth Place: | Osaka Prefecture, Japan |
| Height: | 1.60 m |
| Weight: | 50 kg |
| Show-Medals: | no |
is a Japanese competitor in synchronized swimming.
She won three bronze medals at the 2015 World Aquatics Championships as well as two silver medals at the 2014 Asian Games. She also won two silver medals at the 2013 Summer Universiade.