||The research objective of this dissertation is to assess the impact that a regional level of foreign policy has on Sino-Russian relations in the 21st century, by successively determining: (1) whether the relations are characterized by power asymmetry at a regional level; and, if yes, then (2) what the main features of that regional-level power asymmetry are; and (3) what influence it has on both actors’ positions in their traditional spheres of influence and on the strategic partnership between them. Based on the regional approach of international relations, the dissertation presents an innovative theoretical model of regional-level power asymmetry along with its three component methodological tools. A complex comparative analysis of China’s and Russia’s hegemonic conditions and penetrations into one another’s traditional spheres of influence shows that during the research period Sino-Russian relations were indeed marked by a regional-level power asymmetry favouring Beijing, which had considerable influence on Moscow’s decline on a regional scale. In the 21st century China has become one of the main threats to Russia’s regional hegemony in the post-Soviet space, as well as the principal external obstacle to the projection of its interests in Northeast Asia. In fact, Sino-Russian regional-level power asymmetry has several additional peculiarities which constitute a threat to Moscow’s strategic positions even beyond these two regions.