Morphometric analysis of mitochondria in skeletal muscles and heart of 6- and 60-month-old naked mole rats (Heterocephalus glaber) revealed a significant age-dependent increase in the total area of mitochondrial cross-sections in studied muscle fibers. For 6- and 60-month-old animals, these values were 4.8 ± 0.4 and 12.7 ± 1.8%, respectively. This effect is mainly based on an increase in the number of mitochondria. In 6-month-old naked mole rats, there were 0.23 ± 0.02 mitochondrial cross-sections per µm2 of muscle fiber, while in 60-month-old animals this value was 0.47 ± 0.03. The average area of a single mitochondrial cross-section also increased with age in skeletal muscles - from 0.21 ± 0.01 to 0.29 ± 0.03 µm2. Thus, naked mole rats show a drastic enlargement of the mitochondrial apparatus in skeletal muscles with age due to an increase in the number of mitochondria and their size. They possess a neotenic type of chondriome accompanied by specific features of mitochondrial functioning in the state of oxidative phosphorylation and a significant decrease in the level of matrix adenine nucleotides.