The paper presents, in a descriptive way Fahreddin er-R?zi’s place, one of the most outstanding figures in history of Islamic thought, in historiography of religious sects in Islam and his contributions to the field. R?zi, as it is known, compiled over two hundred books within almost all branches of Islamic sciences. However, he is well known rather for gigantic works he compiled in the field of commentary on the Koran and Muslim Theology. With our article, we try to analize his work titled “Itik?d?t” its content and method. This work was written especially on the history of Islamic sects, hence is irrelevant to the fields already mentioned, and its distinctive marks in proportion to other works compiled in the same field