What is presented in this article is a report on the content of the principle of Al-Maysūr lā yasqtive bi al-mas‘ur, that is prepared in such parts as introducing the principle briefly, usage in Sh'ite and Sunni jurisprudence law, contents of principle among Sh'ite and sunnis, evidences and reasons of principle among this two sects and also quiddity and its principle jurisdiction. Furthermore, along the description of principle, the author’s criticmis and ideas have also been referred too.