Osek (German: Ossek) is a municipality and village in Strakonice District in the South Bohemian Region of the Czech Republic. It has about 600 inhabitants.

The villages of Jemnice, Malá Turná, Petrovice and Rohozná are administrative parts of Osek.

Osek is a common Czech toponymy. The word osek denotes a cut trunk and it also could mean a cut forest.

Osek is located about 7 kilometres (4 mi) northeast of Strakonice and 52 km (32 mi) northwest of České Budějovice. It lies in the Blatná Uplands. The highest point is a hill at 506 m (1,660 ft) above sea level. There are several fishponds in the municipality; the largest of them are Velký and Bašta. The ponds are supplied by the stream Petrovický potok.

The first written mention of Osek is from 1392, then known as Vosek or Wossek. It was probably founded in the second half of the 14th century. The village began to grow around the lord's court, on which a fortress was probably built before 1414. Osek was acquired by King Wenceslaus IV as escheat. He divided it among his minions.

Until World War I, the villages of Osek, Petrovice, Malá Turná and Rohozná were administrative parts of the municipality of Radomyšl, and Jemnice was a sovereign municipality. Shortly before World War I, the villages separated and created a new municipality. In 1924, Osek was renamed to its current name. In 1961, Jemnice joined the Osek municipality.

Historical population

Year Pop. ±% 1869 1,100 —     1880 1,104 +0.4% 1890 1,040 −5.8% 1900 1,039 −0.1% 1910 916 −11.8%	Year Pop. ±% 1921 956 +4.4% 1930 847 −11.4% 1950 680 −19.7% 1961 779 +14.6% 1970 724 −7.1%	Year Pop. ±% 1980 696 −3.9% 1991 665 −4.5% 2001 600 −9.8% 2011 649 +8.2% 2021 665 +2.5%
Source: Censuses

The I/4 road (the section from Strakonice to Příbram) passes through the municipality.

The railway line Strakonice–Blatná runs through the municipality, but there is no train station. The municipality is served by the station in neighbouring Radomyšl.

The most important monument is the Osek Castle. The fortress from the 15th century was completely rebuilt into the current pseudo-Baroque castle in 1911. It has valuable interiors. Today it serves as a home for people with disabilities. Next to the castle is a park founded in the early 20th century.

• Official website