There is little information about oligodendrocytes (OLGs) in the Periaqueductal Gray matter (PAG). The literature has not provided data on the number, morphology, or quantification of the expression of the OLG protein yet. Myelin Basic Protein (MBP) in this region of the Central Nervous system (CNS). The study aimed was to perform a comparative analysis: the location and morphology of OLGs, the cellular and regional distribution of iron, and the number of OLGs in PAG and corpus callosum (CC) of adult 16 male and 16 female sheep. To determine the location of the OLG of PAG and CC, the method of impregnation of the neuroglia with silver salts was applied. In turn, the Nissl method was used to determine the location of the brain structure and to analyse the number of OLG. The performed analysis showed that PAG, OLGs are located singly or in pairs in blood vessels and neurons, while in CC they are arranged in characteristic rows and accompany both nerve fibres and blood vessels. Immunofluorescent staining for the presence of MBP confirmed the location of OLGs in male and female sheep. Morphometric analysis showed the importance of these glial cells in OLG-myelin fibres, correlation in adults regardless of sex even after the creation of the completion of myelin. The results obtained indicate that the functions of OLGs are not only confined to myelination in young individuals, but also play a crucial role in the brain of adults. Our observations seem to be useful to better understanding OLGs biology.