Dr. Mahdi Haeri is one of Muslim philosophers that considers ontological argument as a valid one. He accepts Anselm’s argument but rejects Descartes and Severely criticises it. One of his arguments is against Descartes belief that God's essence is different from His existence, the other is against taking God's necessity of existence on a par with the necessity of mathematical truths, while the necessity of God’s existence does prove the existence of God. Also, Aquinas  considers  Anselm’s  argument invalid, for Anselm believes the  existence  of  God is self evident, but since we don’t  know the essence of  God, His existence is evident  in itself, but is not evident  for us. Dr. Haeri thinks that this argument is invalid and argues that it isn’t true and replies to that. He argues that first evident propositions are of one kind, not two kinds and secondly for validity of Anselm’s argument, we don't need to know the essence of God, but understanding the verbal definition is sufficient. Dr. Haeri agrees to some of the Kant’s critisims of Deascartes, but not of Anselm. This article deals with Dr. Haeri’s views on Anselm’s and Descartes’ argument, and Aquinas’ and Kant’s critisims of the ontological argument