Duke Frederick of Saxe-Weimar (1 March 1596 in Altenburg – 29 August 1622 in Fleurus, Belgium) was a prince from the Ernestine branch of the House of Wettin and a Colonel in the Thirty Years' War.

Duke Frederick was the son of John II of Saxe-Weimar and his wife Dorothea Maria of Anhalt, sister of Prince Louis I of Anhalt-Köthen.

With his older brother, Duke John Ernest the Younger, he received his first lessons from the tutor and Hofmeister Friedrich von Kospoth.

Prince Louis I of Anhalt-Köthen gave him the nickname der Hoffende ('"the Hopeful'") and the motto it will be so.

[2] In the regiment of Christian the Younger of Brunswick, he tried to break through the blockade of the Spanish troops during the Battle of Fleurus and was fatally wounded.