Bierzwnik [ˈbjɛʐvnik] (German: Marienwalde) is a village in Choszczno County, West Pomeranian Voivodeship, in north-western Poland. It is the seat of the gmina (administrative district) called Gmina Bierzwnik.

It lies approximately 24 kilometres (15 mi) south-east of Choszczno (Arnswalde) and 84 km (52 mi) south-east of the regional capital Szczecin (Stettin).