In the present age, the religious fanaticism among followers of Takfiri Salafism has had a tremendous effect on the sociopolitical evolutions in some Islamic countries. This movement has issued decrees about the exit of Islamic denominations from the realm of Islam and has caused the emergence of numerous violent behaviors in those countries. Thus, understanding the factors for formation of that movement is so important. In this article, we have attempted to deal with the effect of formalism on religious fanaticism in the framework of legal reasoning (ijtihâ, d) as the common framework in understanding Islamic texts. The findings of this study show that the factors leading to formation of religious fanaticism in that movement are as follows: formalist legal reasoning,priority of transmitting hadiths over contextual study of them,Takfiri Salafist approach to following religious experts,and formalist understanding of some religious concepts and doctrines such as association with Gods friends (walâ, ʾ, ) and dissociation from Gods enemies (barâ, ʾ, ), takfî, r (excommunication), tyrant (ṭ, â, qû, t), tatarrus, jihad and the like.