| Country: | DEU |
| Type: | B |
| Route: | 431 |
| Map: | B431 Verlauf.svg |
| Map Notes: | Route of Bundesstraße 431 |
| Direction A: | Northwest |
| Terminus A: | Meldorf |
| Direction B: | Southeast |
| Terminus B: | Altona borough of Hamburg |
| States: | Schleswig-Holstein, Hamburg |
The Bundesstraße 431 (or B 431) is a German federal main road running in a northwest to southeast direction from Meldorf to the Altona borough of Hamburg.