Osowa Sień [ɔˈsɔva ˈɕɛɲ] (German: Röhrsdorf)[2] is a village in the administrative district of Gmina Wschowa, within Wschowa County, Lubusz Voivodeship, in western Poland.

The current name of the village is literally a house in the aspen and appears in Polish historical sources also as Ossowa Sień or Ossowasień.

[4] The Church of St. Fabian and St. Sebastian, built in the 14th century, is the oldest historical building in Osowa Sień.

Inside there is as well the sculpture of Christ from the 16th century and the Renaissance tombstones of a former landlords from Żychliński and Ossowski family.

[5] In the village there is also a neoclassical palace complex built between 1890-1904 and a Classicist manor from the beginning of the 19th century, both surrounded by large park areas.