The aim of the study - to identify differences in the immunohistochemical characteristics of the neurons of the arcuate (ARС), ventromedial (VMH) and dorsomedial (DMH) hypothalamus between young and old rats. Material and methods. The work was performed on male Wistar rats aged 3-4 months and 2-2,5 years using immunohistochemical methods. Results. In DMH, the percentage of calbindin (CB)immunoreactive (IR) of neurons is significantly reduced, and the percentage of calretinin (CR)-IR of neurons increases in DMH and VMH during aging. In old animals, the number of neuronal nitric oxide synthase (nNOS)-IR neurons and the degree of immunofluorescence to nNOS increased in all studied nuclei. In old rats, there is an increase in the density of neuropeptide Y-IR fibers in the VMH and a decrease in the DMH. Conclusions. The neurochemical composition of the nuclei of the middle group (mainly DMH and VMH) of the hypothalamus changes during aging.