Austfjorden is a fjord in Vestland county, Norway. The 20-kilometre long fjord runs along the border between Alver Municipality and Masfjorden Municipality. It starts in Alver 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. The village of Myking lies on the western shore of the fjord, near the innermost part of the fjord.
On the north side of the Austfjorden there are several deep bays. The first of these is the 2-kilometre long Mjangersvågen with the small village of Mjanger the head of the bay.
