Sa'd al-Dawla Tus (Persian: سعدالدوله توس) was the Baduspanid ruler (ustandar) of Rustamdar from 1390 to 1394.
[1] The Baduspanids had been temporarily removed from power after their ruler Adud al-Dawla Qubad (r. 1379–1381) was defeated and killed in 1381 by the Mar'ashis, who incorporated Rustamdar into their own domains, thus extending their sway over all of Mazandaran.
[2] In 1390, the Mar'ashis installed Tus on the Baduspanid throne to challenge the Afrasiyabid prince Iskandar-i Shaykhi who accompanied the Turco-Mongol ruler Timur (r. 1370–1405), who intended to conquer Mazandaran.
However, Tus secretly corresponded with Iskandar-i Shaykhi, and eventually joined the forces of Timur in 1392.
[4] Tus managed to convince Timur to spare the Mar'ashi family; they were deported instead, while Iskandar-i Shaykhi was appointed governor of Mazandaran.