Hattfjelldal is a municipality in Nordland county, Norway. It is part of the Helgeland traditional region. The administrative centre of the municipality is the village of Hattfjelldal. Other villages include Grubben, Svenskvollen, and Varntresk. Hattfjelldal Airfield is located in the village of Hattfjelldal.
Hattfjelldal is one of the last strongholds for the seriously endangered Southern Sami language that has been in use in Scandinavia since the Stone Age.Hattfjelldal was one of the municipalities in Norway involved in the Terra Securities scandal.
The municipality of Hattfjelldal was established in 1862 when it was separated from the large municipality of Vefsn. The initial population of Hattfjelldal was 961. On 1 January 1964, the part of Hattfjelldal on the north side of the lake Røssvatnet (population: 168) was transferred to Hemnes.