The concept of "unity of existence" is one of the most prominent and attractive concepts in Islamic philosphy and mystic. It is assumed that the views of the seventh-centurey gnostics are significant in the elaboration of this concept. Also those views may significantly contribute to further research on this topic. In this respect, the mystical works of Sheikh Aziz Ibne Muhammad- e nasafi, the great Sufi of that centurey may prove as useful sources. His views as a scholar who has creatively and carefully sorted a wide range of ideas concerning unity of existence are highly beneficial to our understanding of the fundamentals of this concept. In this paper attempts are made to examine Nasafi"s taxonomy of the ideas about unity of existence as well as his criteria for classification. Further, the study may shed light on Nasafi"s own positions concerning unity of existence.