Charles Augustus, Hereditary Grand Duke of Saxe-Weimar-Eisenach (Carl August Wilhelm Ernst Friedrich Georg Johann Albrecht) (28 July 1912 – 14 October 1988) was a German prince and head of the Grand Ducal house of Saxe-Weimar-Eisenach.

He was born in Schloss Wilhelmsthal the eldest son and heir of Grand Duke Wilhelm Ernst of Saxe-Weimar-Eisenach and his second wife Princess Feodora of Saxe-Meiningen (1890–1972). His father's reign came to an end on 9 November 1918 as a result of the German revolution. When his father died on 24 April 1923, Charles Augustus succeeded him as head of the House of Saxe-Weimar-Eisenach. Until 1922 Charles Augustus was third in line to the throne of the Kingdom of the Netherlands.

Charles Augustus died at Schienen and was succeeded as head of the grand ducal house by his son Michael.

Charles Augustus was married at the Wartburg castle on 5 October 1944 to Baroness Elisabeth of Wangenheim-Winterstein (Tübingen, 16 January 1912 - Munich, 15 March 2010), daughter of Othmar Baron von Wangenheim-Winterstein and wife Maud von Truetzschler. They had three children:

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