The archeological finds dating from Neolithic Age to late Bronze Age covering 3rd to 1st millennia BCE unearthed in the territory of Mongolia and its neighboring regions have been studied on a comparative basis, where the results of Carbon-14 radiocarbon dating, paleo-anthropological and paleo-genetical laboratory tests were utilized. As a result of this study that utilized the most recent achievements in natural and social sciences led to a conclusion that the direct ancestors of present Mongolians are the owners of slab burials. the owners of slab burial and slab burial culture existed during 10-4th centuries BCE 1200-2400 years ago for about 700 years. During the period of their existence, the pastoral nomadic livestock husbandry, intellectual culture and the production of weaponry were developed intensely. By doing so, the owners of slab burials inherited their culture from preceding cultures. During their history of development, they formed their stable land of habitation and their own culture with particular salient features. The identity of their land habitation, language and culture enabled a vital factor to develop into an independent ethnicity. In this way, the owners of slab burials in 10-4th centuries BCE generated the Mongol ethnicity centralized dominantly on the territory of present Mongolia. The cultural features originated in that period of time have been inherited and developed by modern-day Mongolians. A new postulation that those who established the Xiongnu State were the owners of slab burials and they used to speak proto-Mongol language were raised in this article.