New Hampshire Route 4 is a 3.78-mile (6.08 km) long state highway located in eastern Strafford County, New Hampshire. It runs from downtown Dover northeast through Rollinsford to the Maine state border, where it continues as Maine State Route 4 in South Berwick.

For most of its length NH 4 is signed as an east-west highway. Signage in downtown Dover, over its concurrency with NH 9 and NH 108, is inconsistent as it is sometimes signed north-south. It follows a generally southwest-to-northeast alignment.

NH Route 4 is not the same road as, nor is it related to, nearby U.S. Route 4, which also enters the Dover city limits. This is the only instance of two non-linked highways sharing a number in the state.

Route 4 begins in downtown Dover at the intersection between Silver Street (NH 9) and Central Avenue (NH 108). The three routes run concurrently for about a half mile, until Route 4 splits off in the center of town. From here, Route 4 is signed east–west. The route runs northeast out of Dover for just under 4 miles (6.4 km), and passes along the southern edge of the town of Rollinsford. Route 4 immediately crosses the Salmon Falls River into the town of South Berwick, ME and becomes Maine State Route 4. Route 4 does not intersect any numbered highways between the split with NH 9/NH 108.

The western terminus of NH 4 is not readily apparent, as signage at the intersection of Silver Street and Central Avenue seems to indicate NH 4 continuing westbound along NH 9; however, no further signage for NH 4 exists west of this point so it is likely this intersection is the actual terminus.

The entire route is in Strafford County.