A field experiment was carried out during 2017 and 2018 seasons at the Agronomy Department Experimental Farm, Agriculture Faculty, Assiut University to study the effect of foliar spray time by different zinc oxide nanoparticles concentrations (ZnO NPs) on production of maize. The experiment was laid out in randomized complete block design (RCBD) using strip plot arrangement with three replications. Zinc oxide nanoparticles concentration (tap water without ZnO NPs (control), 100, 200 and 300 ppm) were allocated horizontally, while, application time (8-10 leaves, tasseling and grain filling stages) were arranged vertically. Results show that zinc oxide nanoparticles concentrations did not affected significantly on all the studied traits in the both seasons, Furthermore, the foliar spray time had a significant effect on grain yield fed^.-1 in the both season, grains weight plant in the first season only and number of grains row^-1 in the second season only. Moreover, the interaction between studied zinc nanoparticles concentrations and applications time in this respect failed to be significant at 5% level of probability in the two growing seasons. Whatever, the highest grain yield fed.^-1 mean value in the first season (3090.00 kg) was recorded from maize plants which were sprayed by 100 ppm of zinc oxide nanoparticles (ZnO NPs) at tasseling stage, while the corresponding mean value in the second season (3846.00 kg) was achieved from maize plants which were sprayed by 200 ppm zinc oxide nanoparticles at 8-10 leaves stage.