| Country: | JPN |
| Type: | National |
| Route: | 503 |
| Map Custom: | yes |
| Length Km: | 112.7 |
| Length Ref: | [1] |
| Direction A: | North |
| Terminus A: | in Takamori, Kumamoto |
| Direction B: | South |
| Terminus B: | in Hyūga, Miyazaki |
| Previous Type: | Route |
| Previous Route: | 502 |
| Next Type: | Route |
| Next Route: | 504 |
National Route 503 is a national highway of Japan connecting between Takamori, Kumamoto and Hyūga, Miyazaki in Japan, with total length has 112.7km (70miles).