The article assesses the EU legal system as a unique institutional unit and highlights its features. It deals with the comparative legal aspects of the regulation of the social welfare of migrant workers in the EU and the EAEU. Attention is paid to the study of legislation on social welfare for migrant workers in the EU, as well as the possibility of realizing the experi-ence accumulated within the EAEU. It is emphasized that the use of comparative models con-cerning the social welfare of migrant workers in the EU and the EAEU can be productive, taking into account the analysis of the state and dynamics of the EU's legal policy in its historical development. The authors have analyzed the historical stages reflecting the difference within the EU approaches to the regulation of social welfare relations for migrant workers. The emphasis is on the role of EU administrative institutions, which provide a balancing approach to the key principles and social policy settings, due to the desire to eliminate distortions and possible conflicts between the norms of states. At the same time, EU members have the competence within the existing common standards of financial security obligations to expand the estab-lished standards and this makes the EU's social policy geographically differentiated. It is noted that the allied states, formed on trade and economic grounds, such as the EU and the EAEU, are characterized by an objective desire for a single legal space, with the uni-fication of approaches on the social welfare of migrant workers throughout the Union. Never-theless, in complex interstate unions, it is impossible to abandon the principle of multi-level regulation of social and security relations, and in this sense, the situation in the EU and the EAEU is quite similar. The current state of EU law in terms of regulating the relations under consideration largely preserves national legal regimes, and each of them, through its special legal means, determines a different amount of social rights of migrant workers. In the context of the EAEU, a similar approach should not be considered productive, since it does not contribute to the goals of this interstate association, defined by Article 4 of the Treaty on its creation. Therefore, within the framework of the EAEU, it is advisable to fix as early as possible the uniform standards in the area of social welfare of migrant workers, estab-lishing a relatively narrow range of powers of the member states of the Union.