In this paper we present a results of first comprehensive study of the complete mitogenomes in the Buryats with regard to their belonging to the main regional (eastern and western Buryats); tribal (Khori, Ekhirid, Bulagad, and Khongodor), and ethno-territorial (Aginsk, Alar, Balagansk, Barguzin, Ida, Khorinsk, Kuda, Selenga, Verkholensk, Olkhon, Tunka, and Shenehen Buryats) groups. The analysis of molecular variation performed using regional, tribal, and ethno-territorial divisions of the Buryats showed lack of genetic differentiation at all levels. Nonetheless, the complete mitogenome analysis revealed a very high level of genetic diversity in the Buryats which is the highest among Siberian populations and comparable to that in populations of eastern and western Asia. The AMOVA and MDS analyses results imply to a strong genetic similarity between the Buryats and eastern Asian populations of Chinese and Japanese, suggesting their origin on the basis of common maternal ancestry components. Several new Buryat-specific branches of haplogroup G (G2a2a, G2a1i, G2a5a) display signals of dispersals dating to 2.6–6.6 kya with a possible origin in eastern Asia, thus testifying Bronze Age and Neolithic arrival of ancestral eastern Asian component to the South Siberia region.