The article analyzes the international legal framework for the participation of regional organizations in peacekeeping operations. Based on a review of scientific literature, the author examines the evolution of the legal approaches of the United Nations to international peacekeeping operations, considering the changes in their content in recent decades. The author explores the coupling between the peacekeeping mechanisms of the UN and regional organizations. The main object of the study is the peacekeeping activity of the Collective Security Treaty Organization based on the relevant international treaty. The article is an attempt to assess the political capabilities of a regional organization to expand its influence in the world using formal legal research methods. Three possible formats of a peacekeeping operation based on the Agreement on Peacekeeping Activities of the CSTO are revealed by the author. First, a peacekeeping operation by decision of the Organization within the borders of its member states. Its parameters correspond to the traditional (first generation) peacekeeping missions. Secondly, a peacekeeping operation by decision of the UN Security Council. Its deployment requires a mandate of the international community to endow the CSTO, which allows the implementation of multidimensional (second generation) peacekeeping operation by the forces of a regional organization. The third format of the CSTO peacekeeping operations is the participation of the CSTO in UN peacekeeping operations. The necessary legal framework is established by the recent Protocol on Amendments to the Agreement on the Peacekeeping Activities of the CSTO. The Organization is to endow one of the member states with the mandate to apply its multinational (consolidated) peacekeeping forces to the UN Peacekeeping Capability Readiness System. Thus applied CSTO peacekeeping forces can be involved in solving tasks during the UN peacekeeping operations under the CSTO flag. Based on the analysis of the legal framework for interaction between the United Nations and regional organizations in the field of peacekeeping, the author concludes that the potential for regional organizations to independently conduct multidimensional peacekeeping missions without direct violating state sovereignty or the UN Security Council mandate is significantly limited. The main opportunity for the collective use of the CSTO peacekeeping potential lies in its involvement in UN peacekeeping operations based on the approaches applied within the UN system to the organization of international peacekeeping activities.