The data on mitochondrial DNA (mtDNA) restriction polymorphism in Czech population (n = 279) are presented. It was demonstrated that in terms of their structure, mitochondrial gene pools of Czechs and other Slavic populations (Russians, Poles, Slovenians, and Bosnians) were practically indistinguishable. In Czechs, the frequency of eastern-Eurasian (Mongoloid) mtDNA lineages constituted 1.8%. The spread of eastern-Eurasian mtDNA lineages belonging to different ethnolinguistic groups in the populations of Europe was examined. Frequency variations of these DNA lineages in different Slavic groups was observed, with the range from 1.2 and 1.6% in Southern and Western Slavs, respectively, to 1.3 to 5.2% in Eastern Slavs, the Russian population of Eastern Europe. The highest frequency of Mongoloid component was detected in the mitochondrial gene pools of Russian populations from the Russian North and the Northwestern region of Russia. This finding can be explained in terms of assimilation of northern-European Finno-Ugric populations during the formation of the Russian population of these regions. The origin of Mongoloid component in the gene pools of different groups of Slavs is discussed.