This paper focuses on the religious life of Persia under the rule of the Parthians, and begins with a review of the early theology, such as the worship of the ancestors and Mithraism, and then the discussion of Aryan beliefs such as Zoroastrianism, which explain the origins of this religion and its status for the Persian community and Ashkani monarchs as well. It also refers to the other Aryan beliefs that were popular in the kingdom of Parthia, such as Buddhism which originated from India. Finally, the paper discusses the spread out of the heavenly religions represented by Christianity, and the position of the Ashkani state about the spread of this religion.