The Greco-Serbian Treaty of 1867 is the second attempt to create a military coalition of Christian states in the Balkans, aimed at fighting a common enemy ‒ the Ottoman Empire. The agreement reflected the irredentist policy of the two states in solving the Eastern question, the purpose of which was to expel the Turks from the European continent and prevent the seizure of the Balkan territories by the Great Powers.Russia closely followed and moreover, actively influenced the negotiation process, which revealed a serious conflict of interests around the issue of border delimitation in Macedonia.The study highlights three key issues. The first concerns Russia's position on the provisions of the Greco-Serbian Treaty affecting Russian interests. The second has to do with the details of the negotiation process related to the future territorial division of the European territories of the Ottoman Empire and in particular Macedonia and the Bulgarian population living in the northern part of this territory. The third is devoted to the examination of the intermediary role of Russian diplomats.