Diallel cross was performed among eight maize inbred lines (1-IPA 2, 2-IPA 7, 3–IPA 21, 4-IPA 12, 5-71-5, 6-IPA 6, 7- IPA 3 and 8-IPA-14) in the field of Field Crops Department, College of Agriculture, University of Baghdad, during spring and fall seasons in 1999 and 2000. The objective was to evaluate several maize inbred lines and their crosses, and estimation gene action in several maize characters. In the first season (spring 1999), inbred lines were propagated, while in the fall season 1999, a set of 28 hybrids were developed. Hybrid yield trails were conducted during spring and fall seasons in 2000, using randomized complete block design with three replications. Significant differences were found among several averages and heterosis of studied characters. The plants of the hybrids (1x7) and (3x7) were earlier in tasseling and silking in spring and fall seasons. The plants of the hybrids (4x7), (1x4) and (7x8) had higher ear height. The hybrids (1x3) and (3x6) were superior in leaf area in both seasons. The higher grain yield (99.33 gm/ plant) produced from crosses (5x8) in spring season, while in the fall season the hybrid (1x3) produced the highest grain yields (181.60gm/ plant). The higher degree of dominance and broad sense heritability were found in the grain yield, while the highest narrow sense heritability produced in the silking. The single cross hybrid (1x3) could be promising in the fall season in central Iraq.