Izz al-Din Mas'ud (I) ibn Mawdud (Arabic: عز الدين مسعود بن مودود died 1193) was a Zengid emir of Mosul.

When As-Salih Ismail al-Malik the titular head of the dynasty became ill, he indicated in his will that Izz al-Din Mas'ud should succeed him; when he died in 1181, Izz al-Din rushed to Aleppo, fearing that Saladin the sovereign of Egypt would try to conquer it.

When he arrived to Aleppo, he got into its citadel, took over all the money and the gold and married the mother of As-Salih Ismail al-Malik.

Izz al-Din Mas'ud realised he couldn't keep Aleppo and Mosul under his governance, as Saladin was intent on gaining control of Aleppo, so he reached an agreement with his brother Imad al-Din Zengi II the governor of Sinjar to exchange Sinjar with Aleppo; in 1182 Izz al-Din became the governor of Sinjar.

Peace was made upon the submission of Izz al-Din Mas'ud, who agreed to become Saladin's vassal.