The collapse of the USSR affected the Russian-Iranian relations, governed by bilateral agreements during several centuries. The emergence of “new” independent states in the region, such as Azerbaijan, Kazakhstan and Turkmenistan, changed the geopolitical situation and put a question of the legal status of the Caspian Sea. Russian-Persian and Soviet-Iranian agreements had a centuries-old tradition but they did not draw up a legal status of the Caspian Sea or clarify the procedures of subsursafe management. Those agreements governed only laid down rules of navigation and fishery, without touching the issues of oil and gas field exploration, production and transportation, including pipelines on the floor of the Caspian Sea. It did not fit political and economic interests of Azerbaijan, Kazakhstan and Turkmenistan and stimulate them to unilateral actions. Russia and Iran in turn insisted on saving the former rules and agreements. The absence of Convention on legal status of the Caspian Sea introduced uncertainty in the principles of oil and gas development and export, pushing Caspian countries toward making unilateral decisions. Russia and Iran kept close positions, insisting on following the former agreements. The other Caspian countries did not support that position and adopted a policy aimed at division of the Caspian Sea and asserting a certain control over its hydrocarbons. Close Russian and Iranian positions on legal status of the Caspian Sea became a strong deterrent for Caspian countries to let them divide the sea into national sectors and launch pipeline plans on the floor of the Caspian Sea. As the result Russian and Iranian relations had stabilizing effect in the Caspian region. At the same time, the Russian Federation aimed at following a flexible policy, taking into account the interests of the other Caspian countries. The settlement of the legal status of the Caspian Sea with Kazakhstan and Azerbaijan let Russia improve the relations with its neighbors but was not approved by Iran. Russian-Iranian relations were influenced by a profound effect of some western states, that imposed sanctions against Iran. Moreover, the fact that Iran was neglected when the export hydrocarbons routes were discussed and realized let new Caspian countries strengthen its positions. At the turn of 2015-2016 уears Russian-Iranian relations are on the rise, because of bilateral interest in solving regional issues and developing trade and credit agreements. Prospects of Russian-Iranian further cooperation will be determined by some key factors. There are Iranian energy policy, results of further multilateral negotiations on legal status of the Caspian Sea and the level of hydrocarbons production in “new” Caspian countries, that can strongly influence their international policies. All these factors will affect the further Russian-Iranian relations, because these two countries remain core players in the Caspian region.