| Country: | JPN |
| Type: | National |
| Route: | 251 |
| Map Custom: | yes |
| Length Km: | 148.2 |
| Length Ref: | [1] |
| Established: | 10 July 1956 |
| Previous Type: | Route |
| Previous Route: | 250 |
| Next Type: | Route |
| Next Route: | 252 |
National Route 251 is a national highway of Japan connecting Nagasaki, Nagasaki and Isahaya, Nagasaki in Japan, with a total length of 148.2 km (92.09 mi).