Abstract: The research subject is the relations between the Azerbaijan Republic and the Islamic Republic of Iran in terms of the conflict between Azerbaijan and Armenia over the territory of Nagorno-Karabakh. The authors analyze the position of Iran prior to the escalation of the situation and during the first conflict on the territory of Azerbaijan SSR. The authors focus on the relations between Iran and independent Azerbaijan in 1991 – 1994 and cessation of hostilities in Nagorno-Karabakh. The paper analyzes the relations between Azerbaijan and Iran in the 21st century. The authors use the methods of historical scientific research, particularly, the principle of historicism, which implies the study of interrelations of two states since the moment of its formation, and the analysis of the Iranian leadership’s position on this issue. The authors also use the chronological method to study sources in chronological order; the method of comparative analysis, and the principle of objectivity, which helps detect the key tendencies of development of Iran’s relations with both aggrieved parties. The set of these methods helps come to the following conclusions: Azerbaijan and Iran, the two countries with access to the Caspian Sea, have been approaching since the collapse of the USSR. There have been certain prerequisites for the creation of a strong geopolitical alliance between secular Baku and Shiite Tehran. But Iran’s position on the Karabakh issue has been quite ambiguous. At the present time, Iran is more pro-Armenian. It considers Armenia as a strategically important partner, thus aggravating tense relations with Azerbaijan. However, the relations between Azerbaijan and Iran depend on the paradigm of regional international problems.