According to the history of European diplomacy, Russia's security hinges on its strategic influence in Central and Eastern Europe. With the dissolution of the Soviet Union, Russia's strategy to regain its position and security in Central and Eastern Europe raised concerns among countries in the region. In this regard, the Ukraine crisis in 2014 and the annexation of Crimea by Russia posed serious challenges to the security of the region and Europe as a whole. Consequently, countries in the region turned to forming regionalism patterns characterized by an anti-Russian stance to balance against Russia's power and influence. The Russia-Ukraine war in 2022 further aligned and synchronized anti-Russian behaviors in multilateral regional frameworks. Considering these factors, the question arises: How has anti-Russian regionalism in Central and Eastern Europe threatened Russia's national interests? The research hypothesis posits that anti-Russian regionalism in Central and Eastern Europe has threatened Russia's national interests and security through the political, military, and economic convergence of the regional countries. The research findings indicate that developing strategic relations among Central and Eastern European countries through tripartite cooperation triangles, regional organizations, and multilateral initiatives aimed at balancing against Russia has created military-security, political, and economic threats to Moscow's national interests in the region. The research method is qualitative with an analytical-explanatory approach, using the realist theory of balance of power to explain the subject.