In this study, we indicated that maize grains obtained from the seeds treated with nCu at doses of 20 and 1000 mg/kg DW were safe to feed mice. The mice fed with the maize grains exhibited unaltered morphological and functional properties. Importantly, excessive deposition of hepatic and serum Cu of these mice were not detected, and further parameters including BW gain, hepatic and renal biochemical markers and percentages of infiltrated and active splenic immune cells were also found to be similar to the nCu-20, nCu-1000 and control groups. Interestingly, maize seeds treated with nCu at concentration of 20 mg/kg DW stimulated seed germination and plant growth as well as enhanced grain yield and grain mineral nutrients including zinc and calcium, whereas nCu treatment of seeds at concentration of 1000 mg/kg DW unaltered the physiological parameters of maize plants as compared to control plants. A recent study showed that plant tolerance to excess Cu is mediated through activities of antioxidant enzymes against ROS and Cu binding to the cell wall to induce exudates secretion (20), thus the concentration of nCu at 1000 mg/kg DW would be a tolerance threshold of maize plants. Differently, Cu treatment with dose of 8.0 mM inhibits seed germination and growth of wheat and cucumber plants (26), whereas soils supplemented with 250 mg Cu/kg soil do not affect the growth and development of maize plants due to the capability of the plants to inactivate the free Cu though metal chelation by high-affinity ligands (20). The tolerance mechanisms of plants against metals are high risk factors for human health when these plants are incorporated into the food chain (26). Consequently, treatment of maize seeds with 20 mg nCu/kg DW increased grain yield as well as mineral nutrients in maize, which was safe for mouse feed.