Increasing power of Russia and Britain in Iran and the weakness of Qajar Kings against those two countries excesses, forced Iranian authorities to try to find ways to break political deadlock to prevent any military confrontations which could have irreparable consequences like Gulistan and Turkmenchay treaties. Diplomatic relations with a third force was an option which has been considered and practiced from the period of Iran - Russia wars during Fath-Ali Shah reign. This policy has been done by establishing relations with France during that period. It was an unsuccessful experience, and however it has been considered by the rest of Qajar Kings but they accepted the risk of its re-experiencing by a crucial motivation, and it was a hope for reducing the pressure of Russia and Britain Governments. During the reign of Naser al-Din Shah, to find the way for reducing Russia and Britain Pressures on Iran, as a result of Mirza Taghi Khan Amir Kabir suggestion, which has predicted that this country will be one of world powers in future, the young and newly established Government of the United States of America has been considered and to establish relations with the United States became the main priority of Iranian foreign policy To study the history of Iran – United States of America relations and choosing this country as the third power in Iranian foreign policy during Naser al-Din Shah reign in one hand and to study the mutual incentives of the United Stated government in establishing relations with Iran on the other hand, were the main themes of this research, which has been done by applying the Historical Research method and using Descriptive - Analytical approach based on library resources.