New data on mitochondrial DNA polymorphism among Russian population from five oblasts, located within the main ethnic area of Russians, specifically, Ryazan' oblast, Ivanovo oblast, Vologda oblast, Orel oblast, and Tambov oblast (N = 177) are presented. RFLP analysis of the mtDNA coding region showed that most of the mtDNA diversity in the populations examined could be described by main European haplogroups H, U, T, J, K, I, V, W, and X. Haplogroup frequency distribution patterns in the populations of interest were analyzed in comparison with the European and Uralic populations. Based on the haplogroup frequencies, the indices of intraethnic population diversity, Wright's F(st) statistics, and the values of squared deviation from the mean, as well as genetic distances between Russians and European and Uralic populations were estimated. Analysis of these indices along with the anthropological data provided identification of a number of regional groups within the populations examined, which could either result from the interaction of ancient Slavs with different non-Slavic tribes, or could be caused by the ethnic heterogeneity of the ancient Slavs themselves.