Hearing loss (HL) is a genetically and clinically heterogeneous disorder, with perhaps 1 % (i.e. at least 300) of the total genes suspected of causing deafness. HL is a monogenic disorder with an autosomal dominant, autosomal recessive, X-linked, or mitochondrial mode of inheritance. Nonsyndromic mitochondrial HL is characterized by moderate-to-profound HL, no other systemic findings on history or physical examination, and a mutation in either MTRNR1 or the MTTS1 genes. The A1555G mutation in the MTRNR1 gene is a well established cause of deafness due to aminoglycoside ototoxicity. As material for researches samples DNA of 108 patients with deafness of Russian ethnic accessory and the group of the control consisting of 100 persons have served. Mutation A1555G was revealed at 2,7 % of patients with HL in a condition homoplasmy. From the literature presence of mutation A7445G/C (MTTS1) besides the relative deafness arising in the first decade of life is known. Muta tion A7445G/C was revealed at two individuals from group of the control. It is widely distributed in our country, studying of a spectrum and frequent mutations of genes MTRNR1 and MTTS1 is actual for an estimation of risk of occurrence HL in families where the given mutation is in a heteroplasmic condition, and also development of the circuit of antenatal diagnostics of damages of these genes at a fruit. Our result confirms the importance of determining the prevalence of the mtDNA A1555G and A7445G/C mutations in different populations, and the need for mutation detection before the administration of aminoglycoside antibiotics.