A half-diallel cross among five yellow maize inbred lines was made in 2019 summer season, at the Experimental Farm of Agronomy Department, Faculty of Agriculture, Mansoura University, El-Dakahlia Governorate, to investigate heterosis and combining ability to choose the best parental inbred lines for developing high yielding new yellow single crosses and producing better hybrids. In most cases, the mean squares of the genotypes, parents, crosses, and parents' vs crosses were significant or very significant for the quality attributes, yield components, and yield. The variances in grain yield/plant between the parents and their crosses were very considerable. For every analyzed grain yield, yield component, and quality attribute, the GCA and SCA mean squares were significant or extremely significant, demonstrating that both additive and non-additive types of gene effects were involved in the inheritance of these traits. The ratio of GCA/SCA was less than unity for all studied traits, flashing that the non-additive genetic effects were more important and played the major role in the inheritance of all studied traits. The most excellent general combiners were P3 (Inb. 69) and P5 (Inb. 309) for Kernels No./row and grain yield/plant. The greatest cross combinations were eight crosses for grain yield/plant. Nine single crosses manifested positive and highly significant heterosis over mid and better parents (ranged from 193.95% for cross P₄ X P₅ to 865.36% for cross P₁ X P₄ over mid parent and from 115.70% for cross P₄ x P₅ to 686.13% for cross P₂ x P₄ over better parent) for grain yield/plant.