Rukn ad-Din Mas'ud (died in 1156) was the Seljuk sultan of Rüm (Anatolia) from 1116 until his death. Following the defeat and death of his father, Kilij Arslan I, by Radwan of Aleppo at Mosul in 1107, Mas'ud lost the throne in favor of Malik Shah . With the help of the Danishmends, Mas'ud captured Konya and defeated Malik Shah in 1116. Mas'ud would later turn on the Danishmends and conquer their lands. When he died, Mas'ud was succeeded by his son, Kilij Arslan II.