Nowadays the study of the Islamic extremism problem is increasingly acute due to national security threat. This article presents the author's position on the development of the methodology of the Islamic extremism study. Application of methods of symbolic anthropology by Clifford Geertz (thick description, systematization and formulation of conclusions) when revealing peculiarities of outlook and behavior of extremist organizations’ members in the case of the international religious organizations “Nur Movement” and “Takfir wal-Hijra”. This approach allows us to consider the manifestations of extremist activity as symbolic behavior. Specific features of the definition of ethos and worldview of the members of these organizations are also identified. The content of symbols was formed under the influence of specific culture within a particular extremist organization. Identification of individual and collective symbols in the behavior of individual participants, analysis of their content, and comparison with traditional values of Islam contributes to a holistic view of the socio-political and philosophical positions of the extremist organization.