| Longeau | |
| Pushpin Map: | France#France Grand Est |
| Source1 Coordinates: | 49.0212°N 5.636°W |
| Mouth Coordinates: | 49.1477°N 5.8578°W |
| Progression: | Yron→ Orne→ |
| Subdivision Type1: | Country |
| Subdivision Name1: | France |
| Length: | 37.5km (23.3miles) |
| Basin Size: | 213km2 |
The Longeau is a 37.5km (23.3miles) long river in the Grand Est of northeastern France. It rises in Hannonville-sous-les-Côtes and runs generally northeast to join the river Yron at Jarny.