Magdalene Sibylle of Brandenburg-Bayreuth (27 October 1612 – 20 March 1687) was Electress of Saxony from 1656 to 1680 as the wife of John George II.

Her maternal grandparents were Albert Frederick, Duke of Prussia, and Marie Eleonore of Cleves.

She had three surviving siblings: Anna Maria (1609–1680), wife of Prince Johann Anton I von Eggenberg, Duke of Krumlov; Erdmann August (1615–1651); and George Albert (1619–1666).

She was married to John George, Prince Elector of Saxony, on 13 November 1638 in Dresden.

Magdalene Sibylle had a good relationship with the Swedish royal family (the Queen consort from 1620 to 1632, Maria Eleonora of Brandenburg, was her first cousin) and was able to save the city of Pirna from attack by a letter to the Swedish commander in 1639, during the Thirty Years' War.