This paper focuses on some conflicting aspects of current studies on Ancient Mesopotamian religion. In my view, the history of the studies on Assyriology (mainly philological studies on cuneiform texts from the Ancient Near East including Mesopotamia) can be divided into three major stages. The first stage (ca. 1850-1950) is characterized by a theological interest in parallels between the Bible and the textual and archaeological remains of Mesopotamia. The second stage (ca. 1950-1985) was intended to be free from a theological perspective and to describe the ancient remains without bias. A. Leo Oppenheim, a leading assyriologist at that time, argued in his book Ancient Mesopotamia (1964) that "a Mesopotamian religion should not be written," because the available material was limited. His claim may also have been based on the fact that the different religious elements like myth, prayer, and incantation are often correlated or mixed in the religious texts. His arguments had held influence until Th. Jacobsen introduced the concept of 'the sacred' (first used by Rudolf Otto, Das Heilige, 1917) into Assyriology and wrote his book The Treasures of Darkness. A History of Mesopotamian Religion (1976). This work seems to have prepared the way for a third stage which continues today. In this stage, especially the religious texts including incantations are intensively studied. It is of note that some encyclopedic dictionaries and introductions not only have adopted the concept of 'the sacred' to describe the religion of Ancient Mesopotamia but also have adopted comparative viewpoints in describing religions across regions such as Ancient Egypt, Mesopotamia, Syria, Anatolia, etc. For example, in these cases the correspondent phenomena are all organized under like topics such as deities, myth, offerings, rites, religious personnel, etc. In the field of Religious Studies, scholars are challenged to reconsider the modern concept of religion. Assyriologists as well can benefit from these reevaluations. For example, even the concept of 'the sacred' itself is also something which should be examined critically. In this sense, both the argument of Oppenheim and that of Jacobsen have not yet been convincingly settled. Moreover, we must be careful when we use modern languages for discussing ancient religion. Ancient words for certain religious concepts may never be duly replicated in modern languages.