Gjesåssjøen is a lake in Åsnes Municipality in Innlandet county, Norway. The 4.06-square-kilometre (1.57 sq mi) lake lies about 5 kilometres (3.1 mi) northwest of the villages of Kjellmyra and Flisa and about 6 kilometres (3.7 mi) northeast of the village of Flisa. The village of Gjesåsen and the Gjesåsen Church lie along the eastern shore of the lake.

The lake was designated as a nature reserve in 2003. The lake is surrounded by agriculture which use the lake as a source of water. Gjesåssjøen is an important habitat for a number of bird species. About 150 different bird species were observed at the lake between 1996 and 2006, among these rare species such as the grebe and the greylag goose.

• List of lakes in Norway