Langvatnet is a lake that lies in the municipality of Fauske in Nordland county, Norway. The 5.46-square-kilometre (2.11 sq mi) lake lies about 25 kilometres (16 mi) east of the town of Fauske. The village of Sulitjelma lies on the northeastern edge of the lake. Water from the lakes Kjelvatnet and Låmivatnet flow into the lake from the south and east. The water from Langvatnet flows out through the river Sjønståelva to the west towards the lake Øvrevatnet.