Leirfjorden is a fjord in the municipalities of Leirfjord and Alstahaug in Nordland county, Norway. The 20-kilometre (12 mi) long fjord is located east of the town of Sandnessjøen, between the mainland and the island of Alsta. There is a short strait that connects it to the Vefsnfjorden to the south.

There are two bridges that cross it: Helgeland Bridge in the west and Sundøy Bridge in the south. The village of Leland lies on the northern coast and the village of Sundøy lies on the southern coast.

• List of Norwegian fjords