| Country: | JPN |
| Type: | National |
| Route: | 203 |
| Map Custom: | yes |
| Length Km: | 47.3 |
| Length Ref: | [1] |
| Established: | 18 May 1953 |
| Direction A: | North |
| Terminus A: | in Karatsu |
| Direction B: | South |
| Terminus B: | in Saga |
| Previous Type: | Route |
| Previous Route: | 202 |
| Next Type: | Route |
| Next Route: | 204 |
National Route 203 is a national highway of Japan connecting Karatsu and Saga in Japan, with a total length of 47.3 km (29.39 mi).