The foundation of any government and sovereignty lies in its legitimacy. Legitimacy, on one hand, establishes the right to rule for the governing power and, on the other, leads to the recognition and acceptance of this right by the general public. In Islamic-era Iran, rulers derived their legitimacy from Arab caliphs and, in some cases, through domination or by appealing to ancient historical precedents—until the Mongol invasion transformed the sources of legitimacy. Using a descriptive-analytical method, this study aims to compare the process of legitimization between the Mongol Ilkhanids and the Timurids, based on their utilization of the cultural potential and appeal of Shia Islam.The findings indicate that although both ruling dynasties exploited the potential of Shia Islam for political purposes and cultural assimilation within the majority society, Shia jurists cooperated and assisted the Ilkhanids more than they did the Timurids. This contributed significantly to the growth of Shia Islam, both in terms of the freedom of action for Shias and the union of Shia Islam and Sufism during the Ilkhanid era. On the other hand, both the Ilkhanids and Timurids made extensive efforts to legitimize their rule through the construction of religious buildings and the reflection of religious themes in the architecture of the period.Research Objectives:To examine the process of legitimization of the Mongol Ilkhanids and Timurids based on their use of the cultural potential and appeal of Shia Islam.To investigate how the Ilkhanids and Timurids sought legitimization through the inscriptions on buildings from their respective periods.Research Questions:How did the process of legitimization of the Mongol Ilkhanids and Timurids unfold based on their utilization of the cultural potential and appeal of Shia Islam?How was the legitimization of the Ilkhanids and Timurids reflected in the inscriptions on buildings from their respective periods?