After the Soviet Union fragmentation, the Caspian basin, containing considerable resources especially oil and gas reserves, has gained more geopolitical importance. Iran enjoys a distinguished position in the Caspian region, while deprived from advantages of this position. US tends to isolate the Islamic Republic of Iran because its anti-dominance struggle prevents Iran from enjoying its geo-strategic and geo-economic privileged op-portunities including its unique transit situation. Iran's energy diplomacy in the Caspian basin has failed because of Iran-US antagonism and US efforts to reduce Iran's geostra-tegic position by exerting pressure on the Caspian states to transport energy from routes other than Iran.In this article, we intend to examine which of these two are more impor-tant and influential. The hypothesis we are going to discuss in this paper is: The discre-pancy of Caspian states’ diplomacy and discourse has been one of the main factors of the failure in Iran’s energy diplomacy. Therefore, the main question is: Why Iran's energy diplomacy has not been successful in Caspian Basin?
