According to the teachings of judicial jurisprudence, an oath of declaration is an oath that the petitioner must take in lawsuits against the deceased; So that the right that he claims to prove is on the responsibility of the deceased. The legality of the oath is the place of consensus of the Imamiyya jurists, and thus such an oath is recognized in the related laws (Articles 1333 BC and 278 AD); However, the legislator has not clearly defined the scope of such an oath. The explanation is that in jurisprudential sources, many jurists have considered taking such an oath as necessary only in religious cases, and in contrast to some others, they have believed in taking an express oath in all cases (both religious and objective). This issue, i.e., the scope and scope of taking the oath of affirmation, has been left comprehensive and ambiguous in the relevant laws. Considering the importance of the discussion and considering the existing legal ambiguity, the present research is a problem-oriented research and by adopting a descriptive-analytical method, while explaining each of the statements and analyzing the documents in the problem, finally, the latter point of view according to the applications of the evidence of the chapter and The lack of documentation of the rival's promise is the correct theory of the problem.