Background: Zinc oxide nanoparticle (ZnO NPs) has been widely used in biomedical applications and cancer therapy and has been reported to induce a selective cytotoxic effect on cancer cell proliferation. Methods: Female Swiss Albino mice were inoculated subcutaneously with Ehrlich ascites carcinoma (EAC) cells. ZnO NPs or MTX were injected intraperitoneally. Tumor growth inhibition rate (TIR %), increase in life span (ILS%), zinc concentration, lipid peroxidation marker (MDA), glutathione (GSH) contents, and the activity of the antioxidant scavenger enzymes SOD and catalase CAT was examined. Also, DNA fragmentation and histopathological studies of all groups were carried out. Results: Treatment of tumor-bearing mice with ZnO NPs significantly increased (MST), (TIR %), (ILS %) and reduced tumor weight, compared to tumor-bearing controls. Additionally, Zn concentration and DNA fragmentation were significantly increased in tumor tissues. ZnO nanoparticles were also found to induce oxidative stress, evidenced by the generation of reactive oxygen species and depletion of the antioxidants in tumor tissues, with no changes in the liver. Our data demonstrate that ZnO NPs exert distinct effects via the killing of cancer cells. Conclusion: The study findings demonstrated that the ZnO NPs can induce selective cytotoxicity through reactive oxygen spe­cies generation and oxidative stress.