Radziwiłłówka [rad͡ʑiviu̯ˈwufka] is a village in the administrative district of Gmina Mielnik, within Siemiatycze County, Podlaskie Voivodeship, in north-eastern Poland, close to the border with Belarus. It lies approximately 6 kilometres (4 mi) north of Mielnik, 13 km (8 mi) south-east of Siemiatycze, and 82 km (51 mi) south of the regional capital Białystok.