| 2021 Open de Rennes | |
|---|---|
| Date | 13–19 September |
| Edition | 15th |
| Surface | Hard (Indoor) |
| Location | Rennes, France |
| Champions | |
| Singles | |
 Benjamin Bonzi | |
| Doubles | |
 Bart Stevens / Tim van Rijthoven | |
The 2021 Open de Rennes was a professional tennis tournament played on hard courts. It was the fifteenth edition of the tournament and part of the 2021 ATP Challenger Tour. It took place in Rennes, France between 13 and 19 September 2021.