Iran is a country with technological capability for nuclear fuel cycle. Mainstream theories of nuclear proliferation predict nuclear weaponization of Iran considering its structural, domestic and individual motivations. However, one fact remains that Iran has not yet developed its nuclear weapons. Officially, Iran argues that the Weapons of Mass Destruction, including nuclear weapons, are against principles of Islam. Even though the mainstream theories are sceptical about the influence of religion in security policies of the state, this paper concludes that religious principles have decisive role in nuclear decision-making of Iran. Iran would have gone for nuclear weapons unless it is constrained by religion.