We have assessed the effects of copper oxide nanoparticles on the testis of adult male albino rats, and evaluated the protective potential of EVOO, which has antioxidant properties. The study involved treatment of seventy adult male rats followed by examination of their testis. The rats were divided into four groups (I-V), each contained 20 rats except group II which contained 10 rats. Each of groups (I, III, IV) was subdivided equally into two subgroups (A and B). Rats in group I did not receive any treatment (IA) or injected intraperitoneal (IP) with 0.5 ml of distilled water daily for two weeks (IB). Rats in group II were gavaged 0.4 ml EVOO daily for 2 weeks. Rats in group III injected IP daily for 2 weeks with 0.5 ml distilled water containing 1 mg CuO NPs (subgroup IIIA) and 4 mg CuO NPs (IIIB). Rats in group IV were gavaged 0.4 ml EVOO before IP injected daily for 2 weeks with 0.5 ml distilled water containing either 1 mg CuO NPs (subgroup IVA) or 4 mg CuO NPs (IVB). After treatment, morphological, histological and biochemical studies on the testes were conducted. Examination of CuO NPs treated groups revealed dose dependant increase in pathological changes. These changes were reduced body weight, distorted basement membranes of seminiferous tubules and degeneration of seminiferous cells. Co-administration of EVOO ameliorated most pathological changes. We concluded that CuO NPs induced deteriorating changes in rats' testes which were improved after co-administration of EVOO.