Iran's regional policy in the Persian Gulf and the Oman Sea underwent deep transformations in the 1940s/60s as a result of a series of internal developments and international approaches. The withdrawal of British forces from the Persian Gulf region and the Oman Sea and the emergence of a power vacuum, the issue of Bahrain and the formation of the South Persian Gulf Sheikh Federation were among the most important events that Iran was challenging and confronting in various ways. At the end of this decade, the small emirates south of the Strait of Hormuz, whose foreign and defense policy was managed by England and lacked independent political and administrative focus, demanded the formation of a kind of confederation. Iran opposed the establishment of this confederation. The purpose of this article is to examine the reasons for the strong opposition of the second Pahlavi government to the formation of the Federation of Persian Gulf Sheikhs at this point in time. In the end, it is concluded that due to the presence of Bahrain in this union, which Tehran considered to be part of its sovereignty, Iran opposed it, because from Tehran's point of view, Bahrain was considered a part of the country of Iran, and it was naturally possible to join it arbitrarily. There were no foreign treaties. Iran agreed to it only when the issue of Bahrain and the return of the three islands was concluded after complex negotiations behind the scenes.