This study discusses the views of Fakhruddin al-Razi in his book al-Tafsir al-Kabeer (the big exegesis), or as called Mafateehul-Ghayb (the Keys of the Unseen) concerning some issues related to the monotheism of God Almighty. The article discusses and criticizes these opinions with a brief reference to the most reliable opinion on which the Twelver Shia rely. The main problem that this article discusses is showing the important points of the theological issues that relate to the true monotheism of God's essence and how He is characterized by His attributes, so that His real oneness would not be defected. This issue has played a major role in the Islamic heritage, especially in the theological field, and more specifically in the exegetical heritage of Fakhruddin al-Razi through his explanation of the meanings of Qur'anic verses. The approaches followed in this article are the inductive, analytical, and critical approaches; so, I have induced al-Razi's opinions on these matters, analyzed and criticized them when necessary. The conclusion I have got to in the article is that the doctrinal backgrounds had had a negative influence on al-Razi's thoughts in his interpretation of some of the Qur'anic verses that were strictly related to monotheistic theological questions.