| Image Coa: | Wappen Rennau.png |
| Coordinates: | 52.3°N 65°W |
| Image Plan: | Rennau in HE.svg |
| State: | Niedersachsen |
| District: | Helmstedt |
| Samtgemeinde: | Grasleben |
| Elevation: | 114 |
| Area: | 22.6 |
| Postal Code: | 38368 |
| Area Code: | 05356 / 05365 |
| Licence: | HE |
| Gemeindeschlüssel: | 03 1 54 018 |
| Divisions: | 3 |
| Website: | www.grasleben.de |
| Mayor: | Jörg Minkley |
| Party: | CDU |
Rennau is a municipality in the district of Helmstedt, in Lower Saxony, Germany. The Municipality Rennau includes the villages of Ahmstorf, Rennau and Rottorf am Klei.