A half diallel cross between 8 inbred lines of maize (Zea mays L.) was evaluated under two different nitrogen rates for five quantitative characters i.e. days to 50% silking, no. of rows/ear, no. of kernels/row, 100-kernel weight and grain yield/plant in RCBD with three replications. Nitrogen rates, genotypes, parents, hybrids and parent vs crosses mean squares were significant for all traits under study. Significant parent's x nitrogen rates mean squares were obtained for all traits except, no. of rows/ear and 100-kernel weight. However, insignificant interaction mean squares between hybrid and nitrogen rates were detected for all traits, except days to 50% silking and no. of rows/ear. The mean square associated with general and specific combining ability was significant for all traits except no. of rows/ear in high nitrogen rate (120 Kg n/f). The mean squares of interaction between nitrogen rates and GCA were significant for no. kernels/row. As for days to 50% siliking and for no. of rows/ear, significant SCA x nitrogen rate were obtained.High GCA/SCA ratios which largely exceeded the unity were obtained for 100-kernel weight at low rate of nitrogen fertilization and no. of rows /ear in both nitrogen rates and the combined analysis. The ratio for GCAxN/GCA was higher that ratio of SCAxN/SCA for all traits except for no. of rows/ear. The parental inbred lines no. 3 and 4 were a good combiners for days to 50% siliking and no. of rows/ ear and grain yield/plant. The parental inbred line no. 6 was a good combiner effects for no. of kernels/row, 100-kernel weight and grain yield/plant. For grain yield/ plant, 18 crosses had the highest values for SCA. Also, the cross P1xP3 have significantly out yielded the check hybrid S.C. 162 on both nitrogen rates and the combined analysis. The additive component "D" reached the significant level of probability for all traits except silking date and grain yield/plant at both nitrogen rates. Moreover, the component t2 was significant for both exceptional traits. In addition, the regression coefficients of parental offspring covariance (Wr) on the parental array variance (vr) were significant in both traits to less than unity. Significant values for the dominance component H1 were obtained for all traits. Moreover, values of H1 were significantly larger in magnitude than the respective D values in most cases. Significant "h2" values were obtained in all traits in both nitrogen rates. Values of (H1/4 H2) was that largely deviated from 0.25 were obtained for most traits at both nitrogen rates. The same trend was detected by "F" values. With the exception of no. of rows/ ear, low heritability values were detected for all traits. For no. of rows/ ear moderate heritability values were detected. Over-dominances were obtained by (H/D)0.5 for all traits . Also, the same trend was obtained by wr/vr graph. The array points were widly scattered for all the characters. The parental inbred line no. 1 for silking date, no. 3 and 6 for no. of rows/ ear, no.6 for no. of kernels/row, no. 7 for grain yield/plant in both nitrogen rates and no.6 and 3 for 100-kernel weight at low and high nitrogen rates, respectively seemed to be carry the most dominant genes responsible for the expression of these traits.