In Islamic culture, the Mu‘tazilite were the first group who employed the rational method and considered the intellect to be the sole means of knowing the truth and to be independent from religion. That is why they have been referred to as the followers of the “religion of the intellect”. The Mu‘tazilite granted a kind of sanctity to the intellect and maintained that when human beings perfect their intellect, they can perceive essential truths, which consist of the knowledge of God and the knowledge of the good and evil. On the other hand, they never denied revelation but believed that it cannot be in contrast to human intellect. They also stated that since the intellect has a longer history than revelation, it is identical with light, without which no one can be led to the right path. The purpose of revelation is to increase intellectual knowledge and make it more accurate. The Mu‘tazilite, thus, concluded that the intellect is the criterion for revelation. This idea was one of their most important principles. Hence, it can be said that, for this group, ethics is based on a kind of intellect which is prior to religion. One of their most famous principles is, “thinking before hearing”. The Mu‘tazilite are mutikallim, and a mutikallim looks at the intellectual human being as a responsible individual before God. They consider the intellect to be sufficient regarding Man’s need to revelation at the outset of obligation. This paper deals with Mu‘tazilites’ view of the relationship between religion and ethics.