This article seeks to identify and explain the process of securitizing ISIS by the Islamic Republic of Iran. The mostimportant question of this article is: How did the Iranian government manage to portray ISIS as an existential threat to itscitizens and how to involve them in their foreign and military policies against this terrorist group? This article uses thesecuritization theory to explain the Iranian war with ISIS in Syria and Iraq. It aims to consider the process and dynamics ofsecuritization of ISIS in Iranian society which led them to support the military combat with ISIS. The research hypothesis isthat the focus on securitization theory prepares the constant framework for understanding how the Copenhagen notion of security helps the Iranian government to justify the enemy narrative of ISIS through the trend of exclusion, exceptionalities, and use of physical force. Iranian government actively uses the securitization process to make required changes and adjustments for confronting ISIS to gain support and legitimacy from ordinary people. This article considers the role of the audience in the process of decision-making and how rulers use this opportunity to mobilize and organize armed forces. The Iranian government in the process of securitizing ISIS has shown that it can involve the people in the process of decision-making and the implementation of its foreign and military policies.