Without doubt, the most important human intellectual system which is now accepted by majority of human beings is monotheistic system of thought. In this paper, the monotheistic thinking of Zaroaster has been investigated through "GATHAHA" or hymns. Also included are "Vadaha", the views of Greek philosophers as well as Indian scholars and finally the political and religious events in Sasanid era. The reflection of monotheistic views of Zaroaster in Farabi and Sohrevardi"s thoughts as well as Farabi"s social pyramid and Sohrevardi"s philosophical pyramid are explained.