Gamma radiation is commonly used to disinfect agricultural products to increase shelf-life. However, this may exert adverse effects on plant growth, development, fertility, and crop production due to oxidative stress and cellular damage. Post irradiation protection using nanoparticles could reduce or reverse deleterious effects after exposure to ionizing radiation. We monitored the effect of zinc oxide nanoparticles (ZnO NPs at 500, 2000, 4000 mg/L) on Vicia faba grown from seeds treated with gamma rays (20, 50, 100 Gy). Phenotypic (seed germination, percentage of inhibition, seedling growth) and cytogenetic markers (chromosomal behavior in mitosis, meiosis and pollen grains) along with ultrastructural changes in the chloroplasts and nuclei (transmission electron microscopy) were assessed. At 20 Gy radiations, ZnO NPs had no effect on the final germination percent; however, at 100 Gy and post-treatment with 4000 mg/L of ZnO NPs, a substantial reduction occurred. While vegetative growth and fruit production increased with 500 and 2000 mg/L ZnO NPs, all three doses of gamma rays induced reduction. ZnO NPs provoked a significant increase in the mitotic index of root meristems compared with the control and gamma radiation. A radioprotective effect of ZnO NPs in the mitotic-meristematic root tips of V. faba was observed. The degree of mutagenic efficiency and pollen grain sterility was dose-dependent. Chloroplasts and nuclei treated with higher concentrations of ZnO NPs (4000 mg/L) and the three doses of gamma rays showed adverse ultrastructural changes. An amelioration or modulation of these changes was observed post irradiation with 500 and 2000 mg/L ZnO NPs. ZnO NPs at 500 and 2000 mg/L concentrations had protective effects through the reduction of adverse effects of all doses of gamma rays at the phenotypic, cytogenetic, and cellular ultrastructure levels. Additional studies are warranted to explore ZnO NPs as potential nano-irradiation protective agents.