The concept of “border” in political literature is a modern concept and in historical literature, the term “frontier” and in ancient times, the concept “frontiers” is used to determine the territory. The neighboring of Iran and the Ottoman Empire (Turkey) in different historical periods has caused different conflicts and disputes between the two countries. A number of factors such as religious differences, expansion desires of the Ottoman Empire and interventions of European powers like Britain and Russia, and most importantly, the lack of exact determination of the boundaries are among the most important factors in collisions between the two countries. The foreign relation between Iran and Turkey during the 1st Pahlavi era was bettered by solving long territorial and cultural disturbances the result of which was a 16-year (1941-1925) close relation. After a 5-week stay in Turkey, Reza Shah came back to Iran. This travel influenced him a lot, so that, since then, some of his reforms, which had already almost been founded, were formed in social and cultural fields. In this era, little by little, the foundation for conducting regional treaties such as Sadabad Regional Treaty which was considered unique in the whole east was provided. This era was in fact a modern period for making an almost vast relation in other fields such as cultural, social, economic, political, et relations. Finally, Iran and Turkey came to the conclusion that, for the survival of their existence, they should put aside differences and become friends and stabilize their borders. The present study explores the borders of Turkey and Iran during the first Pahlavi era, its history and stabilization process of the Turkish and Iranian borders.