This study aims to compare the constitutional standards of Polish and Ukrainian tax law systems. The initial hypothesis has been adopted that there are significant similarities in the systemic solutions applied in both countries, which indicates the existence of processes of both the constitutionalization of tax law and the convergence of their legal systems. Considering that both processes are not yet completed, there is a need to establish systemic standards that are common and possible differences in their regulation. The research problem determines the choice of methods necessary to solve it. The dogmatic method will make it possible to determine the legal acts in force and their content. Whereas the comparative method enables comparison of the constitutional standards of Polish and Ukrainian tax law.