The subject of the research is the problem of ethnogenesis and early ethnic history of the Sakha people. The issue of the research is interaction of the Sakha people’s ancestors with Turko-Mongol ethnic groups of the Baikal region, the comparative method being the methodology applied. The Sakha people’s tribal composition and ethnonyms are subject to the comparison with the names of the medieval Turko-Mongol tribes of the Baikal region and modern Turko-Mongol peoples. The main result of the research is the conclusion about an organic connection between the Sakha people’s origin with the ethnic history of the medieval tribes of Central Asia. The results of the research can be used in writing a new conception of Yakutia’s history. The conclusions obtained are the following ones. Firstly, the analysis of the Yakut ethnonyms helped to trace ethnocultural parallels with the neighboring nations: the Buryats, the Evenks and the Evens, and the Yukagirs. Secondly, the main role in the ethnogenesis of the Sakha people was played by the Usutu-Mangun tribe, the carriers of Ust’-Tal’kinsk culture of the Southern Angara Region of the XII-XIV centuries. Thirdly, the Usutu-Manguns descended from the Buir-Nur Tatars, defeated by the Mongols’ and Jurchens’ united army. Therefore, the article presents numerous parallels between the Central Asian Tatars and the Sakha people. Fourthly, along with the Angara River Tatars the Barga, the Khori-Tumats, the Batulin people, and, probably, the Merkits, etc. played a vital role in the Sakha people’s ethnogenesis.