The author considers two key issues: (1) The Union State of Russia and Belarus: problems and prospects of the Union economy in the new economic conditions; (2) Analysis of the parameters of the effectiveness of the development of the Union State of the Republic of Belarus and the Russian Federation under sanctions. The purpose of the study was to analyze the effectiveness of the development of the Union State of Russia and Belarus in the new economic conditions. To achieve this goal, it have been applied the methods of formal logic, economic and statistical analysis, correlation analysis by influence factors and an expert survey in Google docs. It is shown that, on the one hand, the expected integration unification of the economies of fraternal countries did not justify the hopes. This is due to a combination of reasons-factors, among which the author identifies the four most significant: 1. The initial inequality of the positioning of both countries in the global economy. 2. Different attitudes to the market model in the economy for both countries. 3. Different models of statehood in the economic system of Russia and Belarus. 4. Russia's special status for Belarus as assistance in ensuring security. The above-mentioned factors historically initially create an unequal starting position of fraternal countries, contribute to the formation of various political economic models of Russia and Belarus (the author identifies at least five such models in the system of economic policy of Belarus and Russia), eventually complicating their integration. On the other hand, official statistics show that economic sanctions have a generally positive effect on the state of the economy and the social environment in Belarus and Russia. This is happening, as the results of the expert survey show, due to the internal consolidation of the resources of both countries. Economic sanctions make it possible to generate and implement new tools to stimulate the socio-economic development of the Union economies and other spheres of public life, to identify new priority vectors of joint work. Accordingly, the author summarizes that the strength of the fraternal countries lies in further deepening the socio-economic integration of the Union State of the Russian Federation and the Republic of Belarus.