Abstract: This article is dedicated to examination of the role of Parliamentary Assembly in development of the Union State. The goal is to trace the parliamentary activity in the Union State throughout the entire time of its existence, the objectives that were pursued, their transformation, and change of conditions for their accomplishment. This topic is especially relevant in the current context. A new milestone has passed in the history of Union State: December 2019 marked twenty years since its creation. Agreement on the formation of Parliamentary Assembly of the Community of Belarus-Russia Union State was signed earlier, in 1996. The novelty of this works consists in comprehensive and detailed analysis of different stages in formation of Parliamentary Assembly, which allows describing their role in further consolidation of the Union State. The scientific problem of this article can be articulated as follows: Parliamentary Assembly is not just a legislative institution that formulates the agenda for development of the Union State; it is also a platform for a continuous dialogue between Russia and Belarus. Therefore, examination of this government institution in an urgent scientific problem that allows revealing the key aspects of evolution of the Union State. As the resources for this article, the author explored the legislative acts of the Republic of Belarus and the Russian Federation, legal information from official portals of the Union State and the Parliamentary Assembly. This underline the need for further development of parliamentarism in Russia-Belarus Union State for the purpose of improvement and strengthening of relations between the countries in the current conditions of international transformation. The article is based on most relevant documents pertaining to Russia-Belarus relations for the period from 1991 to the present.