Abstract: This article analyzes the ways of legitimation that are characteristic to the Russian-language propaganda of the terrorist group “Islamic State” that is banned in Russia. The arguments the extremist propaganda resorts to are revealed on the example of the online magazine “Istok”: founded on Muslim law, legitimation on the basis of Quranic texts, appeal to moral justice of the establishment of “Caliphate”, and positioning of “Caliphate” as the traditional sovereign state with its attributes. Description is given to the peculiarities of the Russian-language jihadist propaganda and radical discourse of the “Islamic State” overall: an important distinctive feature of the Islamist propaganda is the archaic motives. Having studied the propagandistic materials, the author outlines such features of jihadist propaganda as propensity to determinism and fatalism, orientation towards eschatological worldview, reference of the logical and political arguments to the times of the establishment of Islam. Application of the methods of political linguistics to the information product of terrorist organization reveals the basic strategy of legitimization of the “Islamic State”, which resorts to the archaic, establishment of the “caliphate” of Islamists to the time of origination of Islam and the era of the “righteous caliphs”. The elements of the traditional state are largely translated onto the external, non-Muslim environment: coverage of the activity of the administrative structures of Islamic State, demonstration of the own economic system, and abundance of national symbols. The analysis of propagandistic materials allows concluding on the nominal role of the leader of the jihadist group Islamic State Abu Bakr al-Baghdadi, whose name is associated not only with the phenomenal success of the jihadist project, but also the equally painful defeat that the “Islamic State” suffered in the end.