A half diallel set of crosses among six inbred lines of maize were evaluated under two plant densities (23333 and 35000 plants/fad) for grain yield and its components and quality traits at Sherenkash Village, Talkha district, El-Dakahlia Governorate. Obtained results are as follows: 1- Highly significant variances due to general and specific combining ability for all studied yield and yield components and quality traits, except ears number per plant and protein percentage under both plant densities and oil percentage under normal plant density. 2- The GCA/SCA ratio was less one for all studied yield and yield components and quality traits under both plant densities, suggesting that non additive genetic action was more important than additive, except rows number per ear, kernels number per row and 100-kernel weight under stress plant density. 3- GCA effects showed that the lines R24, R25 and R39 were good general combiners for grain yield per plant under normal plant density. 4- SCA effects showed that the best F1 cross combinations were P1xP2, P1xP4, P1xP6, P2xP3, P3xP5 and P5xP6 for grain yield per plant. These crosses had highly significant estimates of SCA effects under normal plant density. 5- The highest value of heterotic effects relative to mid and better parents for grain yield per plant  were obtained by P4xP5 followed by P5xP6. These crosses had the highest positive significant heterotic under both plant density.