Izz ad-Din Mas'ud I bin Mawdud (Izz ad Din Bin Qutb ad-Din Mawdud Bin Imad ud-Din Zengi; Arabic: عز الدين مسعود بن مودود; died 1193) was a Zangi emir of Mosul.
He the brother of emir Saif ad-Din Ghazi II, and the leader of his armies. When his brother died 1180 he became the governor of Aleppo. When As-Salih Ismail al-Malik got sick, he indicated in his will that Izz ad-Din Mas'ud should succeed him; when he died in 1181, Izz ad-Din rushed to Aleppo, frearing that Salahu'd-Din will try to conquer it, and when he arrived to Aleppo, he got into its Castle, took over all the money and the gold and married the mother of As-Salih Ismail al-Malik. He knew he couldn't keep Aleppo and Mosul under his governance, as the eyes of Salahu'd-Din were on Aleppo, so he reached an agreement with his brother Imad ad-Din Zengi II the governor of Sinjar to exchange Sinjar with Aleppo; in 1182 Izz ad-Din became the governor of Sinjar, in 1193 he went back to Mosul where he got sick and died. He was succeeded by his son Nur ad-Din Arslan Shah I.