The institutions of leniency in the Islamic Penal Code of Iran, as tools for managing criminals and reducing the social harms of crime, have been influenced by modern criminology teachings. Criminology teachings emphasize that the individual circumstances of the offender, especially in cases where provocation and external circumstances played an important role in committing the crime, should be considered in reducing the punishment. On the other hand, reducing the punishment based on supporting the victim is another important principle of criminology that is analyzed in this article. Modern criminology emphasizes the importance of compensating the victim and protecting his rights. This approach is also reflected in the Islamic Penal Code, and there is a possibility of reducing the punishment in the event of compensation and reconciliation with the victim. The purpose of the present study is to study the criminology of the institutions of leniency in the Islamic Penal Code of Iran, which are the institutions of leniency in the Islamic Penal Code. The research method in this study is descriptive-analytical, and the results of the study indicate that modern criminological teachings have effectively influenced the institutions of leniency and postponement of sentencing in Iran, but there is still a need to complete and develop these institutions to achieve the goals of restorative justice and prevention of recidivism.