Although Ibn Sina is known, as a great philosopher, some of his works imply some significant mystical and theosophical elements. In this article, Ibn Sina's viewpoints concerning the theory of "Essentialism" have been examined.Based on the mystics' reports, the Essentialists claim that despite of their differences in time occurrence and place and also the differences in the religious and cultural traditions, mystical experiences have some similarities. It seems evidently that Ibn Sina can be classified as an Essentialist, but at least he is different from them in the following two main cases: 1) Methodologically, Ibn Sina has a philosophical and aprior approach, but Essentialists, especially Stace, have a posteriori one. 2) Ibn Sina has not mentioned anything about the "paradoxicality", while Essentialists have.These significant differences result from the fact that Ibn Sina is a really noble philosopher and paradox cannot have a position in a philosophical system.According to Ibn Sina, mystical experience is a kind of "immediate knowledge" in which the mystic extract the universally intellectual realities from the "Active Intellect". Because of the theoretical and practical perfection, the mystic achieves a degree which is called "Blessing Intellect" ("Aqle-Mostafad"). Afterward, it is connected to the active intellect, and because of this connection he can observe the universal realities. The mystical experience in Ibn Sina's opinion is at most an objective experience in all parts of which the mystic can observe God. In other words, the mystic in his observations and experiences, can reach the "Unity of Intuition", but not "Pantheism".