ABSTRACT Background: Zinc oxide nanoparticles (ZnONPs) are one of metal nanoparticles that have widespread use in many fields. Objective: To investigate the effect of ZnONPs on cerebellar cortex of rats through histological and immunohistochemical study. Materials and methods: Thirty adult male albino rats were divided into three groups; group I (control), Group II (ZnONP-1 treated group) which received orally 50 mg/kg of ZnONP for two months and Group III (ZnONP-1I treated group) which received orally 200 mg/kg of ZnONP for two months. Specimens of the cerebellar cortex were processed for histological and immunohistochemical study. Morphometric and statistical analysis were carried out. Results: Group II showed Purkinje cells were crowded in many layers surrounded by perineuronal vacuoles and had pyknotic nuclei. They had cytoplasmic vacuoles and perinuclear Golgi apparatus revealed fragmented dilated cisternae. Nearby Bergmann astrocyte cells had highly vacuolated cytoplasm and the nerve fibers were also affected and showed dysmyleination (disrupted myelin sheath). Immunohistochemical study of the same group showed Purkinje cell cytoplasm had positive immunoreactions for calretinin proteins. In group III, there was a wide spread of neuronal affection to the degree of loss of many of Purkinje cells leaving empty spaces. Ultrastructurly, their cytoplasm appeared with multiple variable sized and had dilated mitochondria with disrupted cristae. The Bergmann astrocytes revealed nuclei with disrupted nuclear envelope and nearly absence their cytoplasmic organelle and there was more affection to the nerve fibers in the form of vacuolated axoplasm and demyelination (areas of myelin loss) beside dysmyleination. Immunohistochemical study of group III showed Purkinje cells cytoplasm with negative immunoreactions for calretinin proteins. Conclusion: Intake of ZnONPs induced various adverse alterations in the histological and immunohistochemical structures of cerebellar cortex indicating the occurrence of neurotoxicity. These changes were exaggerated with increasing the dose of their intake.