In this paper, I would like to examine the ancient religions of Iran and Pakistan (India), two key Asia-Aryan countries, surrounding the thought of ‘Complete union of Brahman and Atman’, the most important concept in the religion or philosophy of India-Aryan. In other words, I describe the Zoroastrianism (Mithraism) and Brahmaism (known as Brahmanism), which are rooted in the Aryan tribes. Although ancient Persia and India (i.e., Iran and Pakistan) are the central Asia-Aryan countries, concept of ‘Complete union of Brahman and Atman’ has not been discussed from the perspective of the Aryan people. There seems to be an aspect that this thought has remained as an abstract concept. This paper aims to discuss in more detail by analyzing the historical and geographical background and the religious influence relationship between two countries, focusing on the fact that they are the religions rooted in Asia-Aryan people before separation of its tribe. In Mithraism and later Zoroastrianism, the greatest influence on Brahmaism is its connection with karma and reincarnation, which are the biggest characteristics of Brahmaism. As a result of ‘Good Deed’ on earth in Mithraism, the meaning that the most prudently selected good soul lives at the highest point of heaven is related to Karma(Deed) and reincarnation in Brahmaism. It is commensurate with the most central thought of Brahmaism. In Mithraism, the good soul rises and flies to heaven, while the evil spirit transfers to the body of beast and suffers the torture of hell, which is compared to the wheeling of reincarnation in Brahmaism. The concept of ‘Complete union of Brahman and Atman’ is regarded as one of the most difficult fields in Eastern and Western religious thought. From the Asia-Aryan point of view, the relationship between Mithraism and Brahmaism has been distorted, and it is urgent to restore it.