The question about the causes of developing and continuing hostility between the Islamic Republic of Iran and Israel has become one of the concerns of scholars of foreign policy and international relations. Most works on this issue are based on a positivist attitude. But it should be noted that enmity between these two political units during the past three decades could not be explained by using a positivist approach. This article tries to find that which factors have made Israel the enemy of the Islamic Republic if Iran? Our hypothesis is that considering Israel as an insider in the framework of Pahlavist foreign policy has played a significant role in constructing Israel as the "other" in the Islamist discourse of Imam Khomeini′s foreign policy. To explain this hypothesis, the authors uses the theory of discourse advocated by Laclau and Mouffet and especially the concept of "otherness". Since this theory lacks an instrument for text analaysis, the authors employ the method elaborated by Fairclough to do their research. Their finding is that since the emergence, evolution and development of discourses are carried out under the heavy shadow of the "other", an entity with double function of preventing identity from being established and objectified and of constructing identity and being responsible for discursive coherence, Israel as the "other" has play the role of a constitutive outsider in giving an identity to Islamist foreign policy discourse as opposed to Pahlavist other
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