Being guilty in criminal law is one aspect of criminal proceeding and being prosecuted and punished is another one. In fact, it is on the basis of procedural rules that crime is proved and the offender is sentenced and punished. What is of significant importance in proving the crime and culpability of the accused is 'burden of proof of the crime and the presented defenses' in criminal trial. The burden of proof is the answer to the question that which person or authority should prove his claim in criminal trial. What is discussed in here is not the existence of proof but the important is the responsibility and duty to prove it. Should the prosecution undertake the burden of proving his claim, in case of not succeeding in it, the defendant will be acquitted. Conversely, if it is the defendant who should bear the burden of proving his claim, in case of failure to provide adequate and appropriate proof, he will be sentenced. Obviously, the outcome of trial is in close connection with placing the burden of proof upon the defendant or the prosecution. The general rule in criminal prosecution puts the burden of proof of constituting elements of crime on the prosecution. Iranian Constitution considering this important matter has allocated its Article 37 to the 'presumption of innocence' which says: "Innocence is the basic principle. No person is considered legaly guilty, except in cases where his guilt is established in a competent court" and thus the defendant is exempt from proving his innocence. But in respect of the defenses including justifications and excuses, it's the defendant who claims existence of them during the commitment of crime. The question raised here is that in spite of the presumption of innocence, is the burden of proof of the existence of justifications and excuses on the defendant? or is it the duty of the prosecution, as the public authority of prosecution, to prove all elements of crime and absence of all impediments to prosecution and punishment? This question becomes even more important when the new approach of criminal law considering crimes such as economical crimes and security crimes, moves toward limiting the presumption of innocence and wastage of suspected persons rights.