Introduction: Testosterone is a steroid hormone secreted by gonads and adrenal glands. High dose of testosterone leads to decrease neurogenesis and induce apoptosis in vitro. To modulate testosterone effect, plants contain anti-androgenic properties can be useful. Urtica dioica, often called common nettle, contains anti-androgen compounds. Furthermore, the phytoestrogens effects of nettle have been evaluated. In this study, the effect of nettle root extract on histological structures of the cerebral and cerebellar cortices of rats was evaluated after testosterone injection. Materials and Methods: Twenty healthy adult male Wistar rats were divided randomly into 4 groups: control group (received ordinary feed without any treatment), testosterone group (received 10 mg/kg testosterone subcutaneously), nettle root extract group (received 50 mg/kg nettle root extract orally), nettle + testosterone group (received 50 mg/kg orally nettle root extract and 10 mg/kg testosterone). After 6 weeks, the brains were stained by hematoxylin and eosin. The number of neuronal cell body, nuclear diameter of neurons, diameter of Purkinje cells, and diameter of cerebellar layers were measured. Results: There were no significant differences in the mean number of neuronal cell body in cerebral cortex, diameter of Purkinje cells in cerebellum, and thickness of cerebellar layers among different groups. The nuclear diameter of neurons in inner granular layer of cerebrum in the testosterone group significantly increased compared to the nettle and nettle + testosterone groups. Conclusion: Nettle plant can be considered as a testosterone modulator. To determine more precise effect of nettle on the brain, further studies are needed.