The Principle of legality of crimes and punishments (nullum crimen, nulla poena sine lege) refers to the fact that an act is not considered a crime and deserves no punishment, unless the Legislator determines and announces the criminal title and its penalty before. The legality principle protects individual security by ensuring basic individual liberties against the arbitrary and unwarranted intrusion of the state. Thus, the criminal judge cannot call the individuals' acts crime and assign punishments for them or exert punishments that are not prescribed by the Legislator without any letter of law. If an act is morally rebutted or is socially against the public order, it is not regarded as crime and the Legislator is the only authority who can recognize some acts as crime and punish the actor. In Iranian legal system, before the Islamic Revolution and also after it, the Constitution and ordinary laws have explicitly emphasized the observance of the mentioned principle. When there is no text or in the case of the silence or lack of law, the criminal judge is bound to issue the verdict of innocence. In recent years, as a result of the great misunderstanding of the Art.167 of the Constitution, ordinary rules including s. 214 of the Criminal Procedure of Public and Revolutionary Courts Act 1999, and s. 8 of the Revolutionary and Public Courts Act 1994, allowed the criminal judge to refer to the Jurisprudence and religious decrees in order to assign the criminal titles and the related punishments, when there is no text or in the case of the silence or lack of law. This paper attempts to verify this legal base. It refers to the history of the discussion and the articles of the Constitution and the jural sources to indicate that it's necessary to pay more attention to the aforementioned law and the legality principle, which in turn makes it possible to abolish or amend the contradictory laws.