The validity and soundness of the ontological argument, originally formulated by Anselm, is the subject of debate within Western philosophy. While this argument and its methodology have not been widely adopted among Islamic philosophers, it is possible to evaluate validity of its methodology within the framework of Islamic philosophy. This study examines the soundness of the ontological argument's method, irrespective of its specific formulations, based on Suhrawardī's Illuminationist philosophy and Ṣadrā's Transcendent Philosophy. The analysis reveals that within Suhrawardī's Illuminationist philosophy, the ontological argument cannot be validated in any form. However, based on the principles of Transcendent Philosophy, Illuminationist’s arguments against the invalidity of the method of ontological argument is subject to serious contention. Although by rejecting these arguments, it cannot be concluded that the Illuminationist stance on the invalidity of ontological argument’s method is incorrect, evidence from Transcendent Philosophy can be used to affirm the soundness of this method. Thus, several evidences - such as the self-evident truth of the existence of being, the necessity of affirmation of the self-identity of a thing (thubūt al-shayʾ li-nafsihī), the uncaused nature of existence, and reliance of Ibn Sīnā’s argument on concept (mafhūm) for establishing the existence of God - serve as testimonies that intellect can affirm the methodology of ontological argument. Nonetheless, despite these affirmations, Mullā Ṣadrā did not employ this method to prove the existence of the Almighty God.