Mu'ayyid al-Mulk (Persian: م'ید الملک‎) was a Persian bureaucrat, who served as the vizier of the Seljuk sultan Berkyaruq (r. 1092–1105) from 1094 to 1095, and later vizier of the Sejluk prince and contender Muhammad I Tapar from 1099 to 1101. He was the most energetic and gifted of the sons of Nizam al-Mulk, with whom he neared in capability.[1]