Blefjell is a small mountain range located along the border between Buskerud and Telemark in Norway.

It encompasses parts of the five municipalities of Rollag, Flesberg, Kongsberg, Notodden and Tinn.

The mountain area falls off steeply to the west and more gently to the east.

The area is a popular tourist destination, being approximately 1 hour drive from Kongsberg.

The Norwegian Trekking Association has three unattended tourist huts in the area: Sigridsbu, Eriksbu, and Øvre Fjellstul.