This research investigates the concept of "understanding the nature of the crime" within Article 91 of the Islamic Penal Code of 1392 (2013), focusing on the criminal responsibility of adolescents. The study analyzes the jurisprudential-legal, international and Cognitive psychology foundations to explore the objective and subjective criteria for determining an adolescent's lack of understanding of the nature of a crime. Findings indicate that understanding the nature of a crime goes beyond mere awareness of the act itself; it encompasses comprehending the inherent and social reprehensibility of the criminal act and foreseeing its consequences. Furthermore, the research addresses the challenges in establishing the age of criminal responsibility, the differences between fast and slow thinking systems, and the role of cognitive factors such as mental processes, emotional intelligence, and the emotion regulation component in committing crimes, as well as assessing perceptual abilities, which are dependent on neuroscientific knowledge. The study's conclusion suggests that the legislator should amend Article 91 to provide more precise criteria for establishing the understanding of the nature of a crime and consider a gradual responsibility approach for adolescents in crimes subject to Hadd and Qisas penalties. This study emphasizes the necessity of aligning domestic laws with international regulations and establishing specialized committees to evaluate the perceptual abilities and rational development of adolescents.