Due to the transformation, development and progress achieved in this era, the proof of some issues has become very complicated and their diagnosis requires special knowledge and expertise, which will clarify the truth of the issue by providing technical and specialized information. The purpose of this article is to examine the opinions of expert experts in judicial courts in Imami jurisprudence. This is a descriptive and analytical article and has investigated the mentioned question by using the library method. The findings indicate that the expert's opinion is the point of view of an expert and professional person, which the judge uses as a useful tool to resolve legal and criminal cases. The mentioned opinion is not specific to the current law and has been of interest to jurists for a long time in jurisprudence texts under the title of expert opinion. In Islamic law, the opinion of experts is widely considered and in various chapters of jurisprudence, the opinion of experts is widely cited and numerous examples of specialized issues in which it is necessary to refer to experts have been presented. The expert's theory is considered one of the main pillars of the proceedings when it is the basis for issuing a verdict. For this reason, the expert must have certain qualifications and in order to conduct the expert, certain regulations and formalities must be observed by the court and the expert so that the theory of the expert is valid.