The border areas of countries are aimed at playing a special role in the development of general economic and social relations, enhancing the geopolitical significance of regional interstate relations. The purpose of the work is to study and show the modern economic complex of border regions on the example of Russia and Mongolia, in which railway transport plays a significant role. Statistical and analytical comparison as a method of scientific analysis allowed examining in detail the territorial production complex of a large region, its resource dependence, and the conditionality of the functioning by the configuration of transport routes and transport accessibility indicators, both in Russia and Mongolia. The Russian railways, which connect Siberia and the Far East with the European regions of the country, continue to provide interdistrict and interregional economic relations at the present time. The Mongolian railways, which have a smaller length, perform a linking role between the fields of raw materials and the points of its processing or further transportation. The study showed that railways continue to be the basis for interregional cross-border connections. However, as the shortest transport route between the countries of Western, Central, Eastern Europe, and the countries of Central, East, and South-East Asia, the railways of the region in question, uniting the border regions of Mongolia and Russia, can strengthen their role in interstate cooperation and become the most important part of the international Eurasian transport corridors - the Steppe Route and the Silk Road.