Variation in populations of sea otter Enhydra lutris lutris from Komandor islands and Kamchatka was studied in segment b1-b2 of cytochrome b gene and in the control region (main noncoding region) of mitochondrial DNA (mtDNA) by means of restriction analysis. The total sample size was 59 animals. Polymorphism was recorded only in the control mtDNA region for one restriction endonuclease (MboI). Frequencies of polymorphic variants were 64.7 and 35.3%, respectively. The low level of mtDNA variation in the sea otter populations examined is in good agreement with the published data on mtDNA polymorphism in populations of this species from north America. A discrepancy between the level of mtDNA variation and heterozygosity of protein-coding loci was demonstrated.