The Ondřejov Observatory ( [ˈondr̝ɛjof]; Czech: Observatoř Ondřejov) is the principal observatory of the Astronomical Institute (Astronomický ústav) of the Academy of Sciences of the Czech Republic. It is located near the village of Ondřejov, 35 kilometers southeast of Prague, Czech Republic.
The facility was constructed in 1898, by Czech amateur astronomer and entrepreneur Josef Jan Frič as a private observatory. On 28 October 1928, he donated the facility to the Czechoslovak state to celebrate the tenth anniversary of its independence. The observatory, located at an altitude of 500 meters, away from the air and light pollution of urban Prague, was administered by Charles University until the founding of the Czechoslovak Academy of Sciences in 1953, which from then on operated it as part of its Astronomical Institute in conjunction with other Czechoslovak observatories.
It has been responsible, among other scientific achievements, for the discovery of numerous asteroids, more recent works of astronomers from Ondřejov include examination of the trajectory and origin of the Chelyabinsk meteor. More than 700 minor planets were discovered at this observatory. While most of these discoveries are officially credited to the astronomers who discovered them, a remaining 23 minor planets are directly credited to "Ondrejov" (the observatory itself) by the Minor Planet Center for the period 1997–2008.
The main-belt asteroid 7204 Ondřejov, discovered by Petr Pravec in 1995, was named for the village where the observatory is located.