Alija Izetbegovic, who is one of the late Islamic thinkers, is a versatile man of thought and action. In this study, the place of reason and belief, man as a rational being and his aspect of belief, which is one of the most pondered subject of Izetbegovic, is examined. Researches on Izetbegovic are mostly directed to his aspect of man of action. However, before being a man of action, Alija put forward about the position of man in terms of being, knowledge, and ethics in a philosophical manner. Without understanding this side of Alija, it is hard to comprehend his thought on the whole. From this point of view, how the reason and belief aspect of man being is understood has an importance in the thought of Alija. His evidence of God’s existence is similar to evidence of Ithbāt al-Wājib in Theology. He gives physical, biological and anthropological evidents in this matter. So, human being belongs to metaphycial area and couldn’t reduce mechanicism process. Alija distinguishes between man’s reason and his/her heart. Human being researches nature with his reason and produces arts with his heart. Thus our thinker distinguishes categorically between scientific activities and art activities. Alija says that reason cannot say anything for the metaphysical realm. But this situation is open to criticism. As a result of this point of view, he distinguishes between culture and civilization. The same idea applies to morality, which is a matter of value as well. In our study, including various thinkers, the frame of Alija’s views on the subject was tried to be drawn.