Osieck is a town in Otwock County, Masovian Voivodeship, in east-central Poland. It is the seat of the gmina (administrative district) called Gmina Osieck. It lies approximately 20 km south-east of Otwock and 40 km south-east of Warsaw.

History

On 4 June 1981, a collision between two trains occurred near Osieck, killing 25 people. Osieck was deprived of its town rights by the Tsar on June 1, 1869, which was a way to punish the city for the participation of its inhabitants in the January Uprising. On 1 January 2024 after 155 years Osieck regained its town rights.