Gisela Agnes of Rath (9 October 1669, in Kleinwülknitz, now part of Köthen – 12 March 1740, in Nienburg) was Duchess of Anhalt-Köthen by marriage from 1698.

Her paternal grandfather was Wilhelm von Rath, who commanded the army of Prince Louis I of Anhalf-Köthen during the Thirty Years' War.

His mother, Princess Eleonore, tried to end this relationship, because Gisela Agnes was considered lower nobility, and unsuitable to marry a ruling Prince.

Nevertheless, children from this marriage were officially recognized as potential heir to the throne by the Princes of Anhalt in 1698 and the emperor in 1699.

In 1699, Emmanuel Lebrecht gave her the castle, city and district of Nienburg as a personal possession for life.

Gisela Agnes died in Nienburg on 12 March 1740 and was buried in the princely crypt in the St. Jacob church in Köthen.