Austfjorden is a fjord in Hordaland county, Norway. The 20-kilometre (12 mi) long fjord runs along the border between the municipalities of Lindås and Masfjorden. It starts in Lindås and extends to the northwest. The Masfjorden joins the Austfjorden from the north, and then the Austfjorden empties into the Fensfjorden before reaching the open sea near Fedje. The Austfjorden is the innermost arm of the Fensfjorden. The village of Knarrviki and the Mongstad industrial area lie on the western shore of the Austfjorden.