Berżniki is a village in the administrative district of Gmina Sejny, within Sejny County, Podlaskie Voivodeship, in north-eastern Poland, close to the border with Lithuania. It lies approximately 7 kilometres (4 mi) south-east of Sejny and 109 km (68 mi) north of the regional capital Białystok. Berżniki, like Sejny, has been inhabited by Lithuanians since its beginning.