Posterstein is a German municipality in the Thuringian Landkreis of Altenburger Land.

Municipalities near Posterstein are Heukewalde, Löbichau, Nöbdenitz, and Vollmershain in the district of Altenburger Land; as well as Paitzdorf and the city of Ronneburg in the district of Greiz.

Within the German Empire (1871–1918), Posterstein was part of the Duchy of Saxe-Altenburg.

The Postersteiner Burg, which is lit up at night, is the most important building in the town.

The next train station on the rail line from Posterstein is in Nöbdenitz.