Białusny Lasek [bjaˈwusnɨ ˈlasɛk] is a village in the administrative district of Gmina Myszyniec, within Ostrołęka County, Masovian Voivodeship, in east-central Poland. It lies approximately 3 kilometres (2 mi) south-west of Myszyniec, 38 km (24 mi) north-west of Ostrołęka, and 130 km (81 mi) north of Warsaw.