Applying soil N fertilizer is a crucial factor for maximizing maize (Zea mays L.) grain yield. Maize hybrids have been found to positively respond to high amounts of applied soil N; yet high-applied soil N amount results in reduced N use efficiency (NUE), develops more environmental problems, and augments grower economic inputs. One way to compensate for using excessive N fertilizers is to apply non-symbiotic seed-inoculated nitrogen fixers. Therefore, the main objective of this experiment is to study NUE and its components – nitrogen uptake efficiency (NUPE) and nitrogen utilization efficiency (NUTE)-- of three maize hybrids at different N levels, and bio fertilizer. A 2-yr field study was carried out at the Moshtohor Agricultural Experiment Center, Kalubia in 2001 and 2002 on clay soil with a pH 7.85 and 2.0 organic matter. Eighteen treatments were: 0, 60, and 120 kg N f –1; three maize cultivars (C) – Single Cross 10 hybrid (SC), Three-Way Cross 310(WC), and Giza 2--; zero and bio fertilizer (BF). Treatments were arranged as a split plot design in four RCB. The N levels were the main plots, and factorial combinations of both cultivars and bio fertilizer were the subplots. The N rate varied in favor of the 120 kg N, in both years, for all yield components and grain yield. In addition, grain N uptake increased in the same trend and this was reflected in grain protein yield. However, grain NUE, as well as its components, NUPE and NUTE, was inversely related to N rate. Maize SC 10 hybrid, on the other hand, out yielded both TWC 310 and Giza 2 for grain and protein; surpassed both for NUE and NUPE. Addition of bio fertilizer did not cause any differences for all characters studied. Only in both years, the N x C interaction was quite different (p<0.05) for just 100-grain weight and grain yield. Both SC x 60- and x 120-kg N for either 100-grain weight or grain yield had the highest means in both years. By cutting N rate in half within each cultivar, grain yield relatively dropped by 31.5% for Giza 2 and by 32% for SC, and by 37% for TWC averaged over the two years. Within maize cultivar, the 0-N and the two N rates differed for grain protein content, yet within N rate, cultivars had similar response within 0-N but great variation occurred within either 60- or 120-kg N. Grain NUE negatively responded to N fertilizer rate in both years. Mean SC hybrid for NUE were 51.7, 34.5 compared to 43.5, 30.3 for Giza 2; and 37.0, 31.7 kg grain kg –1N for TWC hybrid for 60- and 120-kg N, respectively. Despite both NUPE and NUTE mean values were negatively associated with N rate and this paralleled NUE mean value, NUPE seemed to have contributed relatively more to NUE than NUTE.