Introduction: Zinc oxide nanoparticles (ZnO-NPs) are of the mostly applied nanomaterials, having many biological benefits because of their ultra-small size. However, toxicity appeared with their wide use. Cinnamon is a well-known antioxidant agent traditionally used by many people. Aim of the present work was to inspect the toxic properties of ZnO-NPs on renal cortex in albino rats and the possible ameliorative effect of cinnamon extract. Material and Methods: Three groups of adult male Wister albino rats (15 rats each). Group I (control group), group II was given1 gm/kg/day ZnO-NPs orally for 4 weeks and group III received ZnO-NPs as group II co-administered with 20% w/w methanol extract cinnamon orally for 4 weeks. At the end, rats from all groups were sacrificed & kidneys were excised & processed for histological & ultrastructural study. Results: Group II showed increased fibrous tissue deposition, marked congestion, some necrotic and some degenerated tubular cells. Ultra-structurally, group II tubular cells showed disrupted cytoplasmic basal infoldings, vacuolation of the cytoplasm and many lysosomes. The filtration barrier showed a relatively thick basement membrane. In group III, the renal cortex showed apparently normal glomeruli with signs of regeneration and less fibrous tissue deposition with no ultrastructural changes. Conclusion: ZnO-NPs displayed some toxic effects in the renal cortex of albino rats that were markedly improved by co-administration of cinnamon extract.