Abstract: The post-Soviet countries are one of the main directions of Russian foreign policy, and the problems of national and regional security are key to the current agenda. These issues are dealt with by several international organizations in the region, while their functions overlap and there is no clear coordination between them. As a result, it becomes necessary to set priorities for Russian diplomacy in relation to these organizations. The article compares two international security organizations - the Collective Security Treaty Organization and the Shanghai Cooperation Organization - in terms of their effectiveness as institutions of international relations and compliance with Russian interests. The comparison is made through the history of the formation and development of these institutions, as well as the adopted regulatory documents and ongoing projects of the CSTO and the SCO. The scientific novelty of the research is the preference of one organization over another, while the result of most such studies is a statement about the need to make efforts for their parallel and full development. The author of the article comes to the conclusion that it is expedient to give priority to the development of the CSTO. The conclusion is made on the basis of the original goals of the founders of the organization, the alignment of forces in them, the dynamics of their development, their institutional problems and the elaboration of their conceptual documents.