National Highway 4 or National Road No.4 (10004) (in Khmer ផ្លូវជាតិលេខ ៤) is one of the national highways of Cambodia. With a length of 230 km (140 mi), it connects the capital of Phnom Penh with Sihanoukville in the south-west. Sihanoukville is the only international sea port of Cambodia, making NH4 one of the country's most important highways. The road was built in the 1950s, coinciding with the construction of the port.