| Gronau | |
| Source1 Location: | Gutsbezirk Spessart |
| Mouth Location: | Altengronau |
| Mouth Coordinates: | 50.245°N 9.615°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Germany |
| Subdivision Type2: | State |
| Subdivision Name2: | Hesse |
| Length: | 9.7km (06miles) |
| Basin Size: | 26.4km2 |
Gronau (pronounced as /de/) is a river of Hesse, Germany and a right tributary of the Sinn. Including its left source river Westernbach, it has a total length of 9.7km (06miles).
The Gronau rises in the unincorporated area Gutsbezirk Spessart in the Hessian part of the Mittelgebirge Spessart. It flows into the Sinn at Altengronau.