We discovery of the use of milk form livestock as a means of subsistence was the origin of pastoralism, which was spread all over Eurasia. In this paper, classification of the milk cultural sphere in arid areas of Eurasia is attempted from the viewpoint of the milk processing system. As a result of our case study on the milk processing systems of some 50 tribes, the following results were obtained. Milking and use of milk from livestock originated in Southeast Asia, and those techniques spread to surrounding areas at the stage of milk souring and preservation. Then, the milk processing systems to the north and to the south of latitude 40°N, at an average yearly temperature 15°C, were developed separately. Cream separation, butterfat processing from the cream by heating, use of the fermented milk as the solidifying additive, production of alcoholic fermented milk in northern areas, extraction of fat from the fermented milk by churning, and use of rennet as the solidifying additive in southern areas, were all developed separately. Therefore, we propose the following hypothesis: “the dualism of the milk cultural sphere in and areas of Eurasia”.