Avicenna's views in philosophy have great influence on his medicine. One of the most important of them is the principle of causality and its branches which have been discussed in philosophical books. Before Avicenna, Greek philosophers like Aristotle tried to develop medicine sciences based on philosophical principles to avoid the expansion of superstitious in medicine and medical treatment. So, this article explains the role of philosophy in the view of Greek philosophers especially Aristotle and Muhammad Ibn Zakariyyā al-Rāzī and in the modern medicine as well as the role of Causality in Avicenna's medicine. Like philosophy, Avicenna's medicine is divided into two sections of theoretical and practical. Avicenna prohibited the doctors from interfering the philosophical problems of the second section. Because it is not his main field and the doctors' responsibility is to cure the decease. But his theoretical medicine is based on some philosophical foundations. In this regard and according to Avicenna's view, the real doctor is someone who knows the philosophy well.  Avicenna's views in regard to the causality in medicine are discussed in these sections, four causes, congruence principle, and teleological view in medicine.