| Charles August, Prince of Nassau-Weilburg | |
| Noble Family: | Nassau |
| Father: | John Ernst, Count of Nassau-Weilburg |
| Mother: | Maria Polyxena of Leiningen-Dagsburg-Hartenburg |
| Spouse: | Auguste Friederike of Nassau-Idstein |
| Issue: | Charles Christian, Prince of Nassau-Weilburg |
| Birth Place: | Weilburg |
| Death Place: | Weilburg |
Charles August (Karl August, 17 September 1685, Weilburg – 9 November 1753) was from 1719 to 1753 Prince of Nassau-Weilburg.
Charles August was the second son of John Ernst of Nassau-Weilburg and Maria Polyxena of Leiningen-Dagsburg-Hartenburg. In his youth, he worked as a diplomat for Saxony; for a while he was the Saxon ambassador in Paris. He succeeded his father as Prince in Weilburg on 27 February 1719.
In 1733 and 1734, he commanded the imperial troops on the Rhine as an imperial cavalry general.
In 1737 he assumed the title of Prince, which family had been awarded in 1688. In 1688 the family had not, however, obtained a seat on the princely bench in the Imperial Diet, and in protest, they had not used their title. In 1737, the seat in the diet was finally awarded and Charles August started using his princely title.
Charles August died in 1753 and was buried in the chapel of Weilburg. He was succeeded by his son Charles Christian.
Charles August married on 17 August 1723 in Wiesbaden, Princess Auguste Friederike of Nassau-Idstein (1699–1750), daughter of George August, Count of Nassau-Idstein. They had the following children:
married Prince Simon August of Lippe-Detmold
married firstly in 1760 Princess Carolina of Orange-Nassau daughter of William IV, Prince of Orange (1743–1787)
married secondly in 1788 Barbara Giessen of Kirchheim