The main question in this research is about ISIS in Iraq and the national security of the Islamic Republic of Iran. With the advance of ISIS in Iraq and the capture of some cities and provinces and the declaration of the government and caliphate in the captured cities, the question is raised in the first place that What will be the future of Iraq? In accordance with the answer given to this question, another more important question can be raised and investigated, and that is, what policies and positions should Iran take in the current situation and the possible future of Iraq? And in other words, what should be done against the ISIS phenomenon? In order to answer this question, firstly, it has been said why the internal situation of Iraq is important and vital for the national security of the Islamic Republic of Iran, then the alternative futures of Iraq have been examined considering the phenomenon of ISIS. Finally, it has been concluded that the requirement of the national security of the Islamic Republic of Iran is the decisive but managed support of the Shia government and the Shia groups present in the current government of Iraq and a decisive confrontation with the ISIS group and its leaders. For this purpose, it has been suggested that Iran strictly pursues the policy of eliminating ISIS from the Iraqi political scene by strengthening the Shia groups militarily and without a physical presence in this country. Also, considering the non-diplomatic stances and behaviors and the image created by this group among the people of the countries of the region, its diplomatic capacity (public diplomacy) and its media atmosphere to create differences between the people of neighboring Sunni countries such as Turkey, Qatar and Saudi Arabia.