Using light and electron microscopy, the structural changes in the hippocampus of senescence-accelerated OXYS rats (n = 20) and Wistar (n = 20) were examined in the age aspect. By light microscopy, the neurons with the signs of chromatolysis and hyperchromatic neurons were detected in CA1, CA3 fields and the dentate gyrus of the hippocampus, suggesting the presence of the signs of degeneration already in 4 month-old OXYS rats. By the age of 18 months, severe structural changes occured in all the regions of the hippocampus of OXYS rats. Ultramicroscopically, in 4 month-old OXYS rats the. initial manifestation of destruction of mitochondria and accumulation of lipofuscin granules were found. These changes were shown to progress with age; 18-month-old animals were characterized by more significant degradation of organelles. These findings indicate more pronounced age-related changes of neurons in OXYS rats as compared to those in in Wistar rats.