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).

The settlement was first mentioned in 1364 as Kostricz, a place of Slavic foundation. There has been a castle since the middle of the 13th century. The city has emerged from two medieval manors.

Within the German Empire (1871–1918), Köstritz was part of the Principality of Reuss-Gera. 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. Today, a modern hotel has been built on the site. In January 2023 Bad Köstritz absorbed the former municipality Hartmannsdorf.

Election in May 2014:

• CDU: 9 seats
• The Left: 3 seats
• Free voters (FWG): 4 seats

• Heinrich Schütz House
• Municipal park

• Heinrich Schütz (1585–1672), German composer of the early Baroque
• Heinrich IX, Count Reuss of Köstritz (1711–1780), founder of the middle branch family Reuss-Köstritz
• Julius Sturm (1816–1896), important German poet of late Romanticism, pastor in Köstritz 1856–1885, honorary citizen of Köstritz 1885
• Gustav von Hüfner (1840–1908), German chemist
• Heinrich Sturm (1860–1917), German jurist, politician and from 1908 to 1917 mayor of Chemnitz

• Landkreis Greiz (in English, German, and French)