The aim of this study is to reveal the characteristics and functions of monotheism in Ahmed Shams al-Din Marmarawi’s work called Jami al-Asrar. Its method is literature review and content analysis. Ahmed Shams al-Din Marmarawi, who is referred to with nisbas such asYighitbasi, Saruhani and Marmarawi is the founder of the Ahmadiyya branch, also known as the "Middle Branch", one of the main branches of the Khalwatiyya, which is one of the most widespread sects of the Islamic world, is one of the prominent sufis of the 9/15 th century and one of the most widespread sects of the Islamic world. It is understood from the sources that he had a very respected position both in Manisa and its surroundings, where he lived, in the capital of the state, and in Ahi circles, which are among the sufi groups. Ahmed Shams al-Din Marmarawi is one of the Sufis who wrote works. He wrote all of his works in Turkish, and generally focused on mystical subjects and concepts in these works. Names and attributes of Allah, love of Allah, human, shaykh, dervish, seyr u suluk (journey), dhikr, body, condescension, nafs and its stages, spirit, interpretations of dreams, the visible realm, unseen realm, basis of existence creed, guidance, tawhid, sharia, tariqa, truth, tariqa line, morality and zamima etiquette, manners are some some of the main subjects he deals with. Tawhid, which is the basis of Islamic belief, is a subject that is meticulously emphasized both in other Islamic sciences and in sufism. Tawhid has been evaluated in an exceptional position by the Sufis because it is seen as the basis and the end of Sufi education. The thoughts of the Sufis, who adopt living in accordance with the purpose of creation as the basic rule of their lives, based on the idea of reaching tawhid, which is seen as the main purpose in the creation of man, and the new explanations they bring to the concept of tawhid are very important. Due to this importance, it is seen that the Sufis of the formation period focused on the concept of tawhid, and the author sufis discussed this issue in their works. Zunnun al-Misri, Junayd of Baghdad, Abu Bakr al-Shibli, Abu Hasan al-Bushanji; the author is only a few of the sufis who focus on the concept of oneness, such as Serrac in his work, which can be briefly called al-Lüma', Kuseyri in al-Risalah, and Hucviri in Kesf al-mahcub. Ahmed Shams al-Din Marmarawi one of the Sufis of the tariqats period, is one of the sufis who emphasized the concept of tawhid. In addition to writing an independent treatise called Keşf al-Asrar and Risalah al-Tawhid, in which he gave limited explanations on the subject of tawhid, he focused on the functions of tawhid in his work called Camiu al-Asrar which is the subject of this study. According to him, some of the functions of tawhid are that it is the first key to the door of God, destroying the castle of the nafs, purifying the morals, entering the battlefield like sword of God, and turning the trouble into a cure. In the chapter of tawhid, Marmaravî revealed the idea of tawhid, which he had contacted from time to time in his other works, in a holistic and symbolic language. While doing this, he preferred a poetic way of expression in the relevant section as well as in the rest of the work he dealt with in verse. His preference not only made the narration fluent, but also facilitated the understanding of the issue. He explained tawhid, which is one of the main creeds of the Islamic faith, forms the basis of mystical thought and education, also seems to be relatively difficult to both explain and understand, by comparing it to various abstract concepts and concrete objects. In this context Marmaravî likens tawhid to concrete objects such as the first word, the first key, the door, the solid stone, the strong castle, the owner-breaker, the vanguard, and the sword of Allah. In addition to these, he reveals the features of tawhid such as the reason for forgiveness, the changer of bad thoughts to goodness, transforming bad morals into good morals, temporary instead of repentance, giving eternal life to the inanimate, reviving the dead heart, transforming polytheism into a cure for oneness, saving from the torment of the hereafter, and being a reason for gratitude. It is clear that in this way, he tried to make the concept of tawhid, which seems difficult to understand, more understandable.