| Sauer | |
| Mouth Location: | Altenau |
| Mouth Coordinates: | 51.6°N 8.8°W |
| Subdivision Type1: | Country |
| Subdivision Type2: | State |
| Length: | 29.9km (18.6miles) |
| Basin Size: | 110km2 |
Sauer is a river of North Rhine-Westphalia, Germany. It is a right tributary of the Altenau, which it joins in Atteln.