A half diallel cross among eight yellow inbred lines of maize was made in 2017 growing season. The resulted 28 F1 crosses along with the check hybrid SC166 were evaluated under two sowing dates, i.e. 15th May (normal sowing date) and 1st July (late sowing date) using a randomized complete block design (RCBD) with three replications at the Experimental Farm, Faculty of Agriculture, Kafrelsheikh University in 2018 growing season, to estimate general (GCA) and specific (SCA) combining ability effects as well as to identify type of gene action controlling the inheritance of the studied traits. Data were taken on days to 50% silking, plant height, ear height, ear length, ear diameter, No. of rows/ear, No. of kernels/row and grain yield/plant. The results showed that, the mean squares due to genotypes (G) and crosses (C) were significant for all the studied traits. Moreover, general (GCA) and specific (SCA) combining ability mean squares were highly significant for all the studied traits under both sowing dates. The non-additive gene action played an important role in the inheritance of most studied traits under the two sowing dates. The inbred lines P3 and P5 showed the best desirable GCA effects for earliness and P1 and P2 for shortness and low ear placement. Whereas, the inbred lines P4, P5 and P6 were the best general combiners for grain yield under the two sowing dates. The crosses P1×P5, P2×P4, P2×P7, P3×P6, P3×P8, P4×P5, P4×P7 and P7×P8 had the best SCA effects for grain yield/plant as well as one or more of its components under both sowing dates. The two crosses P2×P7 and P4×P6 had significant and positive superiority over the check hybrid SC 166 under both sowing dates. Therefore, these crosses could be released as commercial hybrids after further evaluation.