One of the most important theological problems in Islamic world consists in the realm of religion, given determined the field of human legislature would become clear. Generally saying, two views may be found in this ground: of majority and of minority. Agreeing with each would have its own effects in legislative system of country. IRI Constitutional Law, being influenced by the former, has intended Divine will to rule over all area of the Iranian`s life. The intention is receivable from various principles of Constitutional Law, particularly from the fourth. The paper, surveying the two approaches, has explained the view of Constitutional Law on the realm of religion and the agents causing its being of majority.