Langvatnet is a lake in the municipality of Rana in Nordland county, Norway. The 26.38-square-kilometre (10.19 sq mi) lake lies just northwest of the town of Mo i Rana. The lake flows out into the river Langvassåga just north of Mo i Rana Airport, Røssvoll. The lake used as a reservoir for the Langvatn hydroelectric power plant in the village of Ytteren, just down the hill from the lake.

• List of lakes in Norway
• Geography of Norway

• Media related to Langvatnet at Wikimedia Commons