Sayn-Wittgenstein-Sayn was a county of Rhineland-Palatinate, Germany, comprising the lands of the region of Sayn.

It was created as a partition of Sayn-Wittgenstein in 1607, although it was not until the next year that it obtained fully the Countship of Sayn.

The succession was never clear, leading to the annexation of the county in 1623 by the Archbishop of Cologne.

It was not until a treaty in 1648 (at the end of the Thirty Years' War) that it was decided the county would pass to the sisters Ernestine and Johanette of Sayn-Wittgenstein-Sayn, under the regency of their mother, Countess Louise Juliane von Erbach (1603–1670).

The branch became extinct in 1846 with the death of Count Gustaf zu Sayn-Wittgenstein-Sayn (1811-1846).