Piastowo [ˈpjastuf] (until 2010 known as Piastów) is a village in the administrative district of Gmina Krzynowłoga Mała, within Przasnysz County, Masovian Voivodeship, in east-central Poland. It lies approximately 17 kilometres (11 mi) north of Przasnysz and 106 km (66 mi) north of Warsaw.

During the Nazi occupation of Poland, it was part of the New Berlin military training area.