Osan (Korean: 오산; Korean pronunciation: [o.san]) is a city in Gyeonggi Province, South Korea, approximately 35 km (22 mi) south of Seoul. The population of the city is around 200,000. The local economy is supported by a mix of agricultural and industrial enterprises.

It is famous for one of the largest markets in South Korea, Osan Market, which has been in continuous operation since 1792.^{[citation needed]} The city was the scene of the first battle between the US and North Korea during the Korean War in 1950; there is a statue and museum dedicated to UN forces on the outskirts of the city.

The United States Air Force base named after the city, Osan Air Base, is not actually located in the city, but is instead 8 km (5.0 mi) south, in the Songtan district (formerly a separate city) of Pyeongtaek.

Osan Station is a large subway station located in the heart of Osan. It is part of the Seoul Subway Line 1 and the KTX. There is a bus terminal next to the subway station and many buses stop in front of the subway station.

Osan came to be called by its current name in 1914, at the time of a general reorganization of local governments under Japanese rule. At that time it became Osan-myeon, part of Suwon. This name in turn was taken from that of a local stream, the Osancheon. However, prior to the Japanese occupation, the name had been rendered in hanja as 鰲山, meaning "soft-shelled turtle mountain." Because of the complexity of the 鰲 ("o") character, and because crows were abundant in the area, the Japanese changed the name to 烏山, meaning "crow mountain school."^{[citation needed]}

The administrative districts of Osan consists of six administrative districts and 24 legal districts. Osan has a population of 228,111 and 97,348 households as of the end of June 2020.

Osan has a humid continental climate (Köppen: Dwa), but can be considered a borderline humid subtropical climate (Köppen: Cwa) using the −3 °C (27 °F) isotherm.

Kyochon, a fried chicken chain, has its head office in Osan.