The brain is of the c nervous system that has drawn the attention of humankind since antiquity. Although there thousands of studies on the brain, Its mysteries have not been fully understood. Neurogenesis has a critical role in the development of the brain. In the current study, we aimed to examine neurogenesis (cell proliferation) by histological and stereological methods in rat brains, as well as the possible effects of age and sex. In our histological assessment, cortical layers were clearly shown and cortex-medulla boundaries were distinguished easily from each other in all groups. The findings obtained from the current study showed that neurogenesis of neurons in rat brains begins to take shape in the early stages of pregnancy and in the organized structure of the neocortex after birth. The primary and secondary thickenings of the cerebral cortex were determined between 1- and 5-week periods, especially in the intrauterine 20th-daygroup and the postnatal 1-week-old groups. These results suggest that adult neurogenesis may also occur in regions within the brain and that the postnatal neurogenesis capacity of neural precursors in the neocortex continues to increase under suitable conditions depending on age.