Sermitsiaq Island (Danish: Sadelø) is an uninhabited island in the Sermersooq municipality in southwestern Greenland. It is one of three mountainous islands located in the middle run of the 160 km (99.4 mi) long Nuup Kangerlua fjord, to the north of Nuuk, the capital of Greenland. The two sibling islands are Qeqertarsuaq Island and Qoornuup Qeqertarsua Island.