Osa [ˈɔsa] is a village in northern Poland, in the administrative district of Gmina Mikołajki, within Mrągowo County, Warmian-Masurian Voivodeship. It lies approximately 5 kilometres (3 mi) north-east of Mikołajki, 24 km (15 mi) east of Mrągowo, and 76 km (47 mi) east of the regional capital Olsztyn.