Projects of the Federal system remain topical in the present political situation. Prospects of federalization are considered in the context of the formation of the Union State of Russia and Belarus. The article reveals the essence of federalism as an integration theory in political and legal spheres. Using comparative analysis, the author reveals the key principles of the organization of the Federal system integration. Supporters of the Federal system rely on the idea of state sovereignty limitation in favor of «higher» sovereignty of the union. The article analyzes the content and evolution of the integration policy of the Republic of Belarus after the collapse of the Soviet Union. This official administrative policy is considered in1995 Republic of Belarus National Security Concept. The author examines the shortcomings of this document, describes the problems of Russian-Belarusian relations in the present period. At the end the article analyzes the prospects for the formation of the federal structure of the Union State of Russia and Belarus.