Mystical ontology is one of the most important issues of theoretical mysticism. Mystics refer to God when they speak about the absolute being. Undoubtedly, the most important mystical ideas of Seyyed Haidar Amoli and Imam Khomeini can be sought in their ontological theories. Sayyid Haider, an eighth-century mystic, was influenced by the views of Ibn Arabi and Imam Khomeini, influenced by the thoughts of Sadr al-Mutallah Shirazi. This research describes and expresses the personal unity of existence, the genuine unity of the same type existence and the absolute being with descriptive-comparative method, and seeks to disclose what they have in common and what make them to differentiate in the ontology as two Shi`tes mystics. Sayyid Haidar, following Ibn Arabi, believes in the truth of a personal unity of its own, and considers the gradation in manifestation. He offering three reasons for the Absolute Being, holds the absoluteness of being. Imam Khomeini, on the other hand, makes the distinction between the being absolute and the absolute being. And he considers the absolute application of the existence rather than the being absolute to be the result of the interplay between concept and object. Following Mulla Sadra's belief, he believes in both a certain form and a manifestation. Following Mulla Sadra's belief, he believes in both a Special gradation and a gradation in manifestation. Sayyid Haidar believes that the existence of the bound is absolute, while the Imam considers the strongest reason to prove the existence of the object as the essence of righteousness.