Foreign policy in post-revolutionary Iran, as other international actors, is affected and transformed by various interior and exterior factors. Emphasizing the Islamist attitude of Iran's constitutional outlook, the present study attempts to reflect on four different stages in foreign policy of the Islamic Republic of Iran: 1. the first year after the revolution; 2. First Republic era (1980-1989); 3. Second Republic (1989-1997); and 4. Third Republic (1997-2005). It is shown that post-revolutionary Iran's foreign policy is simultaneously affected by realistic and idealistic approaches, and any transformation was restricted to the constitutional framework using the same ideological vocabulary. Furthermore, it is shown that all different political parties would like to present their own programs and strategies with regards to the Constitution, the religious doctrine, and Imam Khomeini's stance. It seems that, reflecting on the transformations in Iran's foreign policy, it is necessary to pay attention to the political competition among different parties, and its effects on the process of foreign policy-making in Iran.