Oster is a city located in the Chernihiv Raion of the Chernihiv Oblast in Ukraine. It is geographically situated at the confluence where the Oster River flows into the Desna River.
The city serves as the administrative center for the Oster urban hromada, which is one of the local administrative divisions within Ukraine. As of current records, the population of Oster is 5,564 residents.