The 30-inch sword was found by Goran Olsen, a hiker who found it when he sat down to rest.
Experts say it's in surprisingly good condition after surviving hundreds of years of frost and snow.
The ancient weapon will be able to help archaeologist work out how people lived in Viking times.
The sword will go on display at the University Museum of Bergen.
A twelve hundred year old Viking sword has been found buried in rocks in southern Norway.