The meaning of mental disorder in the Islamic Penal Code is the existence of some severe mental disorders in such a way that at the time of committing the crime, the criminal did not have full will to perform his/her actions and was not aware of the consequences. The main goal of this article is to investigate the role of mental disorders in determining the criminal responsibility of criminals. The research method is descriptive and analytical. The question of this article is that if a person is involuntary while committing a criminal act due to some kind of mental illness and does not have a correct knowledge and understanding of the criminality of her behavior, is he/she considered a criminal? In response to this question, it can be said that according to the Islamic Penal Code approved in 2012, mental illnesses - which are diseases that affect mental and mental health and deprive a person of their will - put a person in a state of insanity and exempt him/her from criminal responsibility. Research findings indicate that not all mental illnesses completely deprive the will. Determining to what extent a mentally ill person is criminally responsible is very important. In addition, the findings of the research showed that the victim suffering from mental disorders could sometimes reduce or increase the punishment of the offender.