The canton Questembert has 16 communes.
| Code | Name | Population ▼ |
|---|---|---|
| 56184 | Questembert | 8 133 |
| 56053 | Elven | 6 651 |
| 56247 | Sulniac | 3 852 |
| 56123 | Malansac | 2 339 |
| 56015 | Berric | 2 129 |
| 56028 | Caden | 1 641 |
| 56135 | Molac | 1 633 |
| 56171 | Pluherlin | 1 542 |
| 56261 | La Vraie-Croix | 1 495 |
| 56254 | Trédion | 1 400 |
| 56111 | Limerzel | 1 370 |
| 56109 | Lauzach | 1 264 |
| 56108 | Larré | 1 104 |
| 56218 | Saint-Gravé | 763 |
| 56045 | Le Cours | 697 |
| 56196 | Rochefort-en-Terre | 647 |