Osiek Jasielski [ˈɔɕek jaˈɕelski] is a village in Jasło County, Subcarpathian Voivodeship, in south-eastern Poland. It is the seat of the gmina (administrative district) called Gmina Osiek Jasielski. It lies approximately 13 kilometres (8 mi) south of Jasło and 59 km (37 mi) south-west of the regional capital Rzeszów.The village has a population of 680.
Osiek Jasielski is located on a hill, some 270 meters above sea level, along the Wisloka river. The defensive settlement of Osiek probably existed since early Middle Ages, guarding southeastern corner of Lesser Poland. In 1365, King Kazimierz Wielki decided to found here a town, together with a castle, with the purpose of defending Poland from possible Hungarian raids. Osiek was the seat of a starosta, and the newly established town was famous for its fairs, which took place twice a year, on April 28 and July 13. Royal bill confirming dates of fairs was announced on Jule 2, 1583, at the market square in Biecz.
Osiek, which until 1772 was part of Biecz County, Krakow Voivodeship, remained a small town. According to some sources, its town charter was voided in 1604, to be returned by King Zygmunt III Waza on March 12, 1618. Most of its residents supported themselves by cultivating land, and the number of artisans was small.
Following the first partition of Poland (1772) Osiek became part of Austrian Galicia, in which it remained until November 1918. In 1934 the government of the Second Polish Republic stripped it of the town charter. During World War II, Osiek was one of stops along the route from General Government to Hungary. The route was used by the Home Army, which was very strong in the area. During Operation Tempest, two bridges were blown up by the Home Army on August 11, 1944, disturbing movements of the Wehrmacht.