The aim of this paper is to study carefully the IbnTaymîyah's three Anti-Mongol fatwâ in connextion with the invasions of Bilâd al-Shâm by Ghâzân Khân. After a substential presentation of the historical back ground of the different innvasion of Syria by the Ilkhanids, the author examines the religious arguments to work out a plan against Ghazan Khan and his fitters who are converted to Islam.The Hanbali scholoar compares the Mongols with the rebelles against Alî b. Abî Tâlib. During the reign of the latter several fitna take place : the battles of Camel, of Siffîn and the emergence of the Kharijits. For the two initial conflicts, the ijmâ‘ of the scholars in religious sciences was requiered. But for the Kharijits it twas not the case. Ibn Taymiyya compares the Mongols with the Kharijites: it is a duty of Islam to fight them. Like the Kharijits the Mongols are the new dissidents of Islam. Finally, the author attempts to date the second fatwâ, very long, who is a tract against Mongol regime.