One of the legal institutions that has always been the subject of much debate in both private and criminal law is “Non-capacity”. Many of these issues, which are rooted in the thoughts of Shia Clergies, have caused controversy among jurists today. Considering that the existing approaches at the time of drafting laws and decision-making in the judiciary regarding the status of protection detainees as vulnerable groups in society are effective, it is important to examine the causes, criteria and principles of the Non-capacity. Therefore, the present article, which comparatively examines the causes, criteria and principles of non-capacity in private and criminal law, seeks to answer the question, what is the difference between the causes, criteria and principles of non-capacity in private and criminal law? The findings of this study indicate that in Iran law, although the legislator has a similar view on the criteria of stone in private law and criminal law, but the causes and principles of non-capacity in private law have a wider scope than criminal law. This shows that the Iranian legislature has a narrow and limited view of this institution in the field of criminal law.