The Islamic world in the Middle Ages witnessed a remarkable activity of Islamic and Jewish mysticism. This common geo-historical and epistemological backgrounds were reflected in the mystical output of the two mysteries. It is clear that there is an interaction between these two streams, as appears in the works of the mystics of that era, especially the Jewish ones. This paper seeks to study one aspect of the mystical interaction between the medieval Islamic and the Jews mysticism which is  the letters and their relation to existence through studying the works of Muhyiddin ibn Arabi and  Sefer Yetzirah (The book of creation) which is one of the most important books of Kabbalah attributed to the Prophet Ibrahim. The study examined the points of convergence and divergence between Sefer Yetzirah and Ibn Arabi by studying several issues on both sides, including: the formative role of the letters, the nature of these letters, their order and their entities or corresponding entities. The study concluded that there are many points of convergence between Ibn Arabi and Sefer Yetzirah, as well as many points of difference. In addition to this, Ibn Arabi’s works covers vaster and more detailed aspects of this subject with reasonable explinations. The study concluded that the possibility of Ibn Arabi being influenced by Sefer Yetzirah is lacking for evidence, especially if we take into consideration that Ibn Arabi relayed on Quran and prophet traditions to support his thoughts. Besides, there is no decisive historical evidence for this claim.