Posejanka [pɔsɛˈjaŋka], 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 4 kilometres (2 mi) south of Sejny and 109 km (68 mi) north of the regional capital Białystok.