Concerning the practice of nomadism and hunting by Mongolian tribes during the period from the eleventh century through the thirteenth century, Б. Я. Владимирцов has speculated that the practice of hunting had survived among them as a trace from their earlier mode of life as forest-dwelling hunters. Hunting had had the important purpose of supplementing food deficiencies at a time when only a few domestic animals were raised, and before their practice of nomadism had fully developed. At that time, the Mongolian tribes had existed thus as what must be called a "nomadic hunting" people. But because the practice of hunting had persisted merely as a remnant of earlier tribal habits, its significance gradually lessened and, by the fourteenth and seventeenth centuries, the economic importance of the practice of nomadism increased in its stead. My own thesis runs contrary to this. I have found that, originally, a species of antelope, wild horses, wild donkeys, tarhaehan and many other various kinds of animals had thrived on the Mongolian steppes. The Mongolian tribes had at that time chiefly protected these wild animals of the steppe. Consequently, the hunting practiced by the Mongolian tribes during the eleventh through thirteenth centuries must be recognized as a peculiar mode of steppe-life ; and hence differing from the form of hunting practiced by forest-dwelling people, supposed to have persisted among them as aremnant of a former forest-dwelling mode of life. From the time of the xiongnu 匈奴, thus, the many nomadic tribes of the Mongolian steppes hunted enthusiastically in the same numbers as their forbears had. Consequently, even later, hunting as practiced by the Mongolian tribes of the eleventh through thirteenth centuries did not easily die away. Even during the fourteenth through seventeenth centuries, hunting continued to be practiced on as large a scale as before. On the other hand, concerning the practice of nomadism, it can be demonstrated that the Mongolian tribes from the eleventh through thirteenth centuries had raised many sheep, goat, cows, horses, etc. And not, as Владимирцов has said, at a time prior to the development of their nomadism. It can be after all assumed that their traditional habits of eating had by that time been already clearly established. From this perspective, it can be seen that the Mongolian tribes during the eleventh through thirteenth centuries had practiced on a large scale a style of hunting appropriate to the steppe, and had also developed a standard style of nomadic life. Economically, these two aspects were jointly essential. The relationship between the two was largely complementary and supplementary. A similar relation between hunting and nomadism also pertains to the economic situation of the later nomadic tribes of the same plateau. In other words, the standards and structure of the economy of the Mongolian tribes during the eleventh through thirteenth centuries were not especially different from the general economic situation of the later nomadic tribes of the same area. As an explanation of the Mongolian tribal economy that formed the basis of the Mongolian imperial state, this thesis has more validity than Владимирцов's.