Radenthein is a town in the district of Spittal an der Drau in the Austrian state of Carinthia. It is situated in the Gegend valley of the Nock Mountains region of the Central Eastern Alps, north-east of Lake Millstatt. The municipality also includes the cadastral communes of Döbriach, Kaning, Laufenberg, St. Peter and Tweng.
The remote forested valley was not colonized until about 1000. Radenthein itself was first mentioned in a 1177 deed as villam Ratehtim, a part of the estates of Millstatt Abbey until its dissolution in 1773. Since the Middle Ages it had been an iron ore and garnet mining area, when about 1908 an extensive occurrence of magnesite was discovered and the foundation of the "Austro-American Magnesite" mining company led to a large increase in population. The municipality obtained the status of a town in 1995.