Ernest II, Duke of Saxe-Gotha-Altenburg was the reigning Duke of Saxe-Gotha-Altenburg from 1772 to 1804. He was the third but second surviving son of Frederick III, Duke of Saxe-Gotha-Altenburg and Luise Dorothea of Saxe-Meiningen. The death of his older brother Frederick in 1756 made him the heir to the duchy of Saxe-Gotha-Altenburg.

Saxe-Gotha-Altenburg was a duchy ruled by the Ernestine branch of the House of Wettin in today's Thuringia, Germany. The extinction of the line in 1825 led to a major re-organisation of the Thuringian states.