Henriette Charlotte of Nassau-Idstein (9 November 1693 – 8 April 1734), was a German noblewoman member of the House of Nassau and by marriage Duchess of Saxe-Merseburg.

Born in Idstein Castle, Idstein, she was the fourth of twelve children born from the marriage of George August, Count and since 1688 Prince of Nassau-Saarbrücken-Idstein and Henriette Dorothea of Oettingen-Oettingen.

[1][2][better source needed] In Idstein on 4 November 1711, Henriette Charlotte secretly married Maurice Wilhelm, Duke of Saxe-Merseburg.

After eight years of childless union, on 23 June 1720, the Duchess gave birth to a daughter, Fredericka Ulrike, who died within hours.

[3][4][better source needed] Although she officially appears as the Duke's daughter, it is highly probable that she was the product of the affair of her mother with Friedrich Carl von Pöllnitz, Henriette Charlotte's Hofmarshal and lover for several years.