Ernest II, Duke of Saxe-Gotha-Altenburg (Gotha, 30 January 1745 – Gotha, 20 April 1804) 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.