Gjesåssjøen is a lake in Åsnes Municipality in Innlandet county, Norway. The 4.06 km2 lake lies about 5 km northwest of the villages of Kjellmyra and Flisa and about 6 km 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.