Fakhr al-Din al-Razi (d. 606/1209), an Ash'arite theologian after Abu Hamid al-Ghazali (d. 505/1111), is a thinker who is influenced by philosophy and also has an inclination to mysticism. The author tries to clarify the role of the interpretation of mi'raj in his thought by examining of his Qur'an exegesis (tafsir), Mafatih al-Ghayb.Mi'raj means the ascension of Prophet Muhammad which is based on Qur'an 17:1, and there are many traditions (hadith) of mi'raj. A later tradition says that Muhammad made the nocturnal journey (isra') from Mecca to Jerusalem riding on Buraq with Gabriel, and ascended to the presence of God, by passing through seven heavens, meeting a prophet at each heaven.In the interpretation of Qur'an 17:1, Râzi proves that the journey of Muhammad was made with both soul and body and it was not a mere vision. In the interpretation of Fatihah, on the other hand, he interprets mi'raj as follows: Muhammad reached God after passing through the two material worlds, the earthly world and the heavenly one, and also experienced spiritual mi'raj, that is, the spiritual ascension from the material world to the invisible one (spiritual world), and to the further invisible world (God). This spiritual mi'raj means the ascendant process of a soul which aims at annihilation (fana'), and man can experience spiritual mi'raj through mystical exercises.This interpretation of spiritual mi'raj is based on his classification of beings. He classifies created beings into that which occupies space, that which resides in subject that occupies space and that which does not occupy space nor does reside in subject that occupies space.It seems that Razi tries to take mysticism into his cosmology which mixes the theological atomism and the philosophical ontology through his interpretation of mi'raj.