| Demnitz | |
| Mouth Location: | Oelsener See |
| Mouth Coordinates: | 52.1479°N 14.4096°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Germany |
| Subdivision Type2: | State |
| Subdivision Name2: | Brandenburg |
Demnitz is a small river of Brandenburg, Germany. It flows into the Oelsener See, which is drained by the Oelse, near Grunow-Dammendorf.