Four maize inbreds (LO1220, B73, NA17 and NA30) and their full diallel crosses were used in this experiment. Parents and crosses were planted at the farm of the Field Crop Department/College of Agriculture/University of Baghdad. Randomized Complete Block Design with three replications used during the spring and fall seasons of 2013 to investigate the effect of three sowing dates (1 July, 15 July and 1 August) to the characters of genotypes and hybrid vigor. Data were collected for number of days to 50% pollen shedding and silking, plant height, ear height and leaf area, the results analyzed statistically and genetically. The results showed sowing date were significant different between the sowing dates 1 July gave the highest values of pollen shedding and silking characteristics. The parent LO1220 and NA17 were earlier in the flowering, while the B73 parent was superior in leaf area, plant height and ear height. the cross NA17×LO1220 was superior in the number of days to 50% pollen release 51.93 days when sown on 1 July while the crosses LO1220×NA17 was superior in the number of days to 50% silking 54.44 day when sown on 1 July. The crosses B73×NA17 was superior in the plant height an average of 139.33 cm when sown on 1 August and given the crosses LO1220×B73 and NA17×B73 were superior in the ear height an average of 72.73 cm when sown on 1 Augest. The results showed that the hybrid vigor was highly significant for characters. The August 14.95% in the reciprocal NA17×B73 for ear height in 1 July. The results of this study revealed that the studied character under dominance gene action.