The long-standing dominance of Iranians over the Persian Gulf and the Sea of Oman and the shores and islands located in that marine area was renewed during the rule of Al-Buyeh. It was after the decline of that dynasty’s power that the Seljuk gained control over the Al-Buyeh’s territory, the Persian Gulf and the Sea of Oman, and, at times, their realm of power extended to the shores of the Roman (Mediterranean) and Qalzam (Red) seas. After the victory over the Ghaznavid in the Battle of Dandanghan in 431 A.H., the Seljuk Turkmen head leaders dominated Khorasan and determined their domain of power and influence in order to gain control over the other provinces of Iran. The Seljuk, who were in charge of military affairs, wisely entrusted the administration of their possessions to the experienced Iranian bureaucrats, and in the light of their military power and utilizing well-considered plans of their Iranian ministers and agents, soon they could prevail on an extended territory. In this chapter, after a brief explanation about the Persian Gulf and the Sea of Oman during the reign of Al-Buyeh, the circumstances based on which the Seljuk Qaward dominated Kerman, captured Oman, and prevailed on the Sea of Oman along with both sides of the straits of Hormuz have been discussed. Subsequently, the mastery of Toghrol Beyk Seljuk over the port of Basra located in the northwest of the Persian Gulf, which took place after the occupation of Baghdad, and their expansions on terrestrial and marine conquests of the great Seljuk Sultans, along with the way the Seljuk dominated Fars, the shores and islands of the Persian Gulf are also among other topics that have been discussed. Finally, the condition of the Persian Gulf and the Sea of ​​Oman during the reign of the Solqori Atabeg is the last topic that has been investigated in this research.