The issue of humoral temperament (mizāj) is mainly a subject of the field of medicine, but it has also been a subject of psychology, philosophy and moral philosophy during time. As the issue is ontologically related to the human nature, it has been dealt from many different perspectives. Within these disciplines, it has been expanded and developed during the historical process. It holds a wide range of literature as it is a rooted and ancient subject analysed within different disciplines. Stretching (...) out to the time of ancient Egypt, this theory was developed in the field of medicine by Hippocrates and by Galen in biology and it was a subject of some of the works of many Muslim scholars, first and foremost Jāḥiẓ, The issue of mizāj, first of all was explained by the theory of four composition (blood, mucus, yellow bile and black bile) Whether the amount of these liquids change within the body has always been an issue of debate according to the conditions of time and the place. Jāḥiẓ, impressed by the views of Galen, has no distinct piece of work on the issue of mizāj. However, he had put forward his views on the changes of the mizāj in some of his works but as he had unarranged writing style, he did not deal with these issues systematically. In this article, we have aimed at systematizing his views, determined in some of his own works and the studies on them, in two stages. What we mean by the change in mizāj is the point of disappearing of the ill temper and bringing good nature instead. Jāḥiẓ, considers the person as the subject of the effort to change the mizāj and evaluates this in two stages. For him, first of all, the person sinks herself into a mental effort. In this process, the person passes through the processes of remembrance, undertaking a task and suggestion. On this point, for abandoning the evilness and adopting the goodness in character, he underlines the importance of reason. Then, are these processes to change the mizāj for Jāḥiẓ are enough? Jāḥiẓ, invites the person to a second effort, accepting the person could feel hardship on the process, based on the analyses of observation and experiment. For this reason, getting a support from outside is proper for him. According to Jāḥiẓ, religion, education, being within the society and political authority are the factors affecting the change in the mizāj. Jāḥiẓ, brings forward views in an approach of taking away almost a general taboo within the society like “once a something always a something”. In an understandable and open wording, he conveys us the stance that the mizāj can change and its applicable within the daily life. In this study, the views of Jāḥiẓ, on the mizāj was evaluated in two stages, the temperament of the person was evaluated on the ground of the change of morality and was considered according to the contributions to the field of Kalam. (shrink)