Niwiski [niˈviski] is a village in the administrative district of Gmina Mokobody, within Siedlce County, Masovian Voivodeship, in east-central Poland. It lies approximately 7 kilometres (4 mi) south-east of Mokobody, 11 km (7 mi) north-west of Siedlce, and 80 km (50 mi) east of Warsaw.