Many international treaties explicitly or implicitly require the determination of national authorities by the contracting parties in order to implement all or part of the treaty obligations, and therefore, it is important to study the process of determining national authorities. In Iran, only the legislative and executive branches have played a role in determining national authorities; In this article, in order to identify the strengths and weaknesses of the Iranian legislature's procedure in determining national authorities, we have analyzed this procedure in a descriptive-analytical way. The result of the study is that due to the silence of the Constitution regarding national authorities, the legislature has, based on the general competence of legislation, the authority to determine national authorities for all international treaties and institutions. Despite this, in many cases, the legislature has left the determination/changing of national authorities to the executive branch, which is critical, especially considering that some of these national authorities are non-executive. Anyway, comprehensive knowledge of the treaty, which is required to determine a national authority, is generally obtained for parliamentarians at the time of ratification of a treaty, and therefore, the most appropriate tool for determining the national authority is the Act ratifying the treaty, but the legislature in rare cases has used these Acts to determine national authorities. Meanwhile ratification of a treaty by the executive branch, which is allowed in some cases, and determination of national authorities in the text of the treaties, have limited the power of the legislature to determine national authorities.