At what point of time Cham people in Vietnam converted to Islam still has a gap of research that needs to supplement. Furthermore, many studies indicated that Champa had been a unified Kingdom on administrative organizations and hadn't had many relationships with other regional context. In the aspect of religion. Hinduism clearly dominated the religious lite or Cham people. Therefore, what point of time and the causes which led Cham people converted to Islam became hard to understand. Basing on the religious history mcthodology. the mcthod of systems-thinking, this article contribuh:d to determine the point of time that Cham people in Vietnam converted to Islam.