Kiersztanowo [kʲɛrʂtaˈnɔvɔ] (German: Kerstinowen; 1938-45: Kersten) is a village in the administrative district of Gmina Mrągowo, within Mrągowo County, Warmian-Masurian Voivodeship, in northern Poland. It lies approximately 8 kilometres (5 mi) north of Mrągowo and 53 km (33 mi) east of the regional capital Olsztyn. Before 1945 the area was part of Germany (East Prussia). The village has a population of 140.