| Province: | NB |
| Type: | NB |
| Route: | 121 |
| Maint: | New Brunswick Department of Transportation |
| Length Km: | 40.08 |
| Length Ref: | [1] |
| Length Round: | 1 |
| Established: | 1968.[2] |
| Direction A: | West |
| Direction B: | East |
| Terminus A: | in Hampton |
| Cities: | Hampton, Valley Waters, Apohaqui |
| Terminus B: | in Sussex |
| Previous Type: | NB |
| Previous Route: | 120 |
| Next Type: | NB |
| Next Route: | 122 |
Route 121 is a mostly north–south provincial highway in the Canadian province of New Brunswick, although it's signed as an east–west highway. The road runs from the Route 1 intersection in Hampton. The road is approximately 40 kilometres, and services small, otherwise isolated, rural communities. In these areas, the highway is often unofficially referred to as "Main Street." The road parallels Route 1 and follows the Kennebecasis River. The highway starts in Hampton as Hall Road, then Main Street. It is also called Main Street in Sussex.
Route 121 was commissioned in 1968 when Route 1 was moved to a new alignment on the south shore of the Kennebecasis River.