Mass'oud Mirza Zell-e Soltan (Persian: مسعود میرزا ظل‌السلطان, "Mass'oud Mirza the Sultan's Shadow"; 5 January 1850 in Tabriz – 2 July 1918 in Isfahan), or Massud Mirza, was an Iranian prince of the Qajar dynasty; he was known as the "Yamin-od-Dowleh" ("Right Hand of the Government").

He was posted as the governor of Isfahan for over 35 years, and the governor of Mazandaran, Fars, and Isfahan for a total of 40 years.

[1] He was the eldest son of Naser al-Din Shah and Effat-od-Dowleh, and the brother of Kamran Mirza Nayeb es-Saltaneh and of Mozaffar ad-Din Mirza (who eventually became Mozaffar ad-Din Shah), but Mas'oud Mirza could not ascend the throne because his mother was a member of the Qajar dynasty.

At the age of thirteen he was appointed the governor of Mazandaran, Turkman Sahra, Semnan, and Damghan for four years.

[citation needed] Zell-e Soltan had 14 sons and 11 daughters including :