The paper is devoted to the problem of international cooperation between the Soviet Union and Japan in the 1920s. The author uses the method of historical and legal analysis to examine the convention on the basic principles of relations between the USSR and Japan that was adopted in 1925. The Convention was one of the first significant historical instruments of the 20th century within the framework of the development of the Russian Far Eastern political program. The author examines the document from a historical and legal point of view in order to reveal its legal component and deepen the understanding of its diplomatic significance and influence on the development of international relations in the first half of the 20th century. The paper presents historical resources on the key reasons and conditions that led to the signing of the Convention. Particular attention is paid to the analysis of the Convention’s content, basic principles of cooperation enshrined in the Convention that laid the foundations for the regulation of relations between the Soviet Union and Japan. The author also examines the consequences the Convention had for both countries both in the short and long run. The study presents the author’s standing regarding the contradictory nature of the Convention of 1925 expressed in realization by the parties of their foreign policy objectives through unequal concessions, particularly for the USSR. The contribution of the Convention to the formation of political and economic relations between Japan and the USSR in the following years is emphasized.