The purpose of the present study is to review the causes of the Seljuk kings’ need for religious and political legitimacy in the state structure and the policy of interaction between the Seljukids and Abbasids. In this regard and using a descriptive-analytic method, this question was answered: what policies and methods were undertaken by the Seljuk government to establish a powerful kingdom and acquire legitimacy from Abbasid caliphs? The results showed that the Turk Seljuks who reached power in Iran at early 5th century, like religious rulers, under the rubric of Islam ruled over Iran and made the highest use of the institution of Abbasid caliphate to justify their religious and political legitimacy and attempted to show their governance in front of people as justified, legitimate, and acceptable. This policy adopted by them had an impact on the state structure and gave direction to that.