The article is devoted to a comparative legal study of the legislation and the practice of its application in relation to the subjects of the right to a constitutional complaint in Ukraine, the Czech Republic and Poland. The author examines the provisions of the Constitutions of the countries, mentioned above, special laws which regulate the right to a constitutional complaint of corresponding subjects, as well as the constitutional courts practice in each of the previously mentioned countries. The study highlights not only a clear list, but also the essence of the subjects of the right to a constitutional complaint in Ukraine, the Czech Republic and Poland through the prism of judicial practice. The author outlined main peculiarities of natural persons, legal entities, in particular legal entities of public law and the state, as well as local self-government bodies as subjects of the right to a constitutional complaint. A significant role is assigned to legal entities and local self-government bodies, because the legislation and judicial practice distinct greatly with regard to these categories of subjects of the right to a constitutional complaint that the legislation and judicial practice in the studied states differ the most. The right of public associations and individuals to file a constitutional complaint on behalf of other (third) persons is also being investigated. The issue of attorneys’ participation in Ukraine, Poland and the Czech Republic both at the stage of preparing constitutional complaints and during court proceedings in each of these countries is revealed. As a result, appropriate proposals were made to improve domestic legislation concerning this issue. Having studied the Czech and Polish approaches to the essence of subjects entitled to a constitutional complaint, the author identified problems and suggestions for improving the relevant legal regulation in Ukraine. In particular, amendments were proposed to Article 56 of the Law of Ukraine “On the Constitutional Court of Ukraine” regarding the definition of the more precise subjects list of the right to a constitutional complaint. Having carried out this comparative legal analysis, the author proposed instances when it is appropriate to grant legal entities of public law and local self-government bodies the right to file a constitutional complaint in Ukraine. The author also provides grounding in irrationality of granting such a right to state bodies in Ukraine because of state administration peculiarities.