Law-making assemblies are one of the institutions involved in the process of policy making. The range of their intervention is from real determination to formal influence. This fluctuation is affected by two categories of structural factors and agents. The structures include the jurisdiction of Parliament, internal organizations of parliament, the power distribution in political systems and external structures which have impact on Parliament. The agents include executive head of parliament, chief executive, representatives and influential groups. Three types of parliament are detectable from relationship of these structures and agents that are determinative parliament, effective, low- of -effect and neutral in the process of policy making. This study is going to investigate the role of Islamic assembly in the process of policy makings in Iran based on the theoretical framework. The results of this study show that assembly had causative, and not determinative, role in regard to structural factors and agents in the process of policy makings.