Dorothea Sibylle of Brandenburg (German: Dorothea Sibylle von Brandenburg) (19 October 1590 â 9 March 1625) was a Duchess of Brieg by marriage. She was a daughter of John George, Elector of Brandenburg by his third wife, Elisabeth of Anhalt-Zerbst. She was also known as Duchess Dorothea Sibylla of Liegnitz and Brieg, and was born as the Margravine of Brandenburg.
Born in Berlin, Dorothea Sibylle was the fourth and youngest daughter of her parents. After her father died in 1598, she grew up in her mother's estate, Crossen (in present-day Poland).
On 12 December 1610, Dorothea Sibylle married her maternal cousin, Duke John Christian of Brieg. She was described as "kind, and religious". She also played a crucial role in her husband's conversion to Calvinism in 1613.
Dorothea Sibylle and John Christian had the following children: