Castell'Azzara is a comune in the Province of Grosseto in the Italian region Tuscany, located about 120 kilometres southeast of Florence and about 50 kilometres east of Grosseto. It occupies the slopes of the Monte Amiata and was once important for the extraction of cinnabar. It was first under the Aldobrandeschi, and then part of the Sforza County of Santa Fiora until 1624.