Ondřejov (Czech pronunciation: [ˈondr̝ɛjof]) is a municipality and village in Prague-East District in the Central Bohemian Region of the Czech Republic. It has about 1,800 inhabitants. The centre is historically significant and is protected by law as urban monument zone.
The villages of Třemblat and Turkovice are administrative parts of Ondřejov.
The first written mention of Ondřejov was in 1352. The Parish church is dated from around the first quarter of the 14th century. In the early modern period it was discovered that there were large amounts of silver ore in the municipality, prompting one of the village's main exports to be crafts such as pottery.In 1850 there were 817 residents and 164 houses, In 1900 974 residents and 169 houses, in 1970 1,024 residents in 248 houses, and in 2016 1,592 residents in 302 houses.
In 1898–1906 the industrialist Josef Jan Frič built the astronomical observatory in the village, which he gave to the Charles University in 1928. Today it is operated by the Astronomical Institute of the Czech Academy of Sciences.