The article examines the complex process of the formation of bilateral relations between the RSFSR / USSR and Iran in the period between the two World Wars. The desire of the parties to establish bilateral relations on an equal, mutually beneficial basis-in accordance with the spirit and letter of the Moscow Treaty of 1921 – is revealed. There are permanent difficulties on the way of rapprochement between the two countries, caused, among other things, by the undisguised interference of England in the internal affairs of Iran. The article reveals the colonial essence of the British policy in Iran, reflected in the Anglo-Iranian treaty of 1921. The Iranian people showed growing dissatisfaction with the British dominance, demanded that the authorities put an end to it, and at the same time called on them to strengthen good-neighborly relations with the RSFSR. The paper traces the main milestones in the development of Soviet-Iranian relations after the state transition in Iran in 1921, and states positive results in bilateral cooperation in political, trade, economic and other spheres. Separately, the anti-Soviet foreign policy of the Shah’s regime at the turn of the 20-30s is traced, which caused great damage to the relations of the RSFSR with Iran. When analyzing the process of Iran’s rapprochement with Nazi Germany, it is emphasized that the pro-German course of Reza Shah Pahlavi not only created problems for the safe existence of Iran, but also, in general, threatened peace and stability in the Middle East.