Hamedan, due to its historical background, geographical location, and communication position in western Iran, was considered one of the important centers of presence and interaction of religious groups. Historical evidence shows that during the period from the fourth century to the beginning of the eighth century AH, movements such as Mazdakiyya and Khormadini, Sunnis with Hanafi and Shafi’i-Ash’ari tendencies, as well as some Sufi sects, were present in different areas of Hamedan. The main issue of this article is to recognize the status of religious groups, examine their changes, and analyze the relationship between religious dispersion and the geographical characteristics of Hamedan during this period. This research was conducted using a descriptive-analytical method and based on library studies and a critical review of historical and sectarian sources. The research findings show that the religious diversity of Hamedan was not simply the result of the historical background of this region, but rather the geographical location, communication routes, and the continuity of social and political interactions have also played an effective role in the formation, persistence, and rearrangement of these flows. Also, the review of sources shows that the representation of some groups in historical texts, in addition to religious realities, has been affected by political conflicts and sectarian labeling.