Bad Köstritz is a town in the district of Greiz, in Thuringia, Germany.

It is situated on the White Elster river, 7 km northwest of Gera.

Bad Köstritz is known for the Köstritzer brewery and its Schwarzbier (black beer).

Köstritz Castle, a four-winged building around a courtyard built between 1687 and 1704, was the seat of a side wing of the ruling House of Reuss, named counts and (from 1806) princes Reuss-Köstritz.

The castle was demolished in 1972 under the government of East Germany, with only the gatehouse left.