Two field experiments were conducted out during 2012 and 2013 seasons to estimate combining ability, heterosis for six inbred lines (Three American inbreds: P97, B73and Oh.43 and three Egyptian inbred lines: R39, Inb.1021 and Inb.1004) and its F₁ crosses. The most important results obtained from this investigation can be summarized as follows: The differences among means of parental inbreds and also among means of crosses were significant or highly significant for all studied traits. Mean squares of crosses were highly significant for all studied traits, indicating wide range of genetic variability among the studied crosses and this is primary requirement for further computation. Both general and specific combining abilities mean squares were found to be highly significant for all studied traits. GCA/SCA variances ratios were found to be lower than unity for six traits i.e. time to tassel emergency, time to silk emergency, number of rows/ear, number of kernels/row, grain yield/plant and shelling percentage and higher than unity for plant height and 100-Kernel weigh. Significant positive general combining ability (GCA) effects were found for most studied traits. The best combiners were P2 (P79) and P4 (Inb.1021) for earliness traits; P5 (Inb.1004) and P6 (Oh.43) for plant height; P5 (Inb.1004) for number of rows/ear; P1 (R39) for number of grains/row; P2 (P97), P3 (B73) and P4 (Inb.1021) for 100-grain weight; P1 (R39) for grain yield/plant; P1 (R39) and P2 (P97) for shelling percentage. Significant positive specific combining ability (SCA) effects were found for most studied traits. The best cross combinations P3×P4 for number of rows/ear; P1×P5 for number of grains/row; P1×P3, P1×P6, P2×P3, P2×P5, P3×P5 and P4×P6 for 100-Grain weight; P1×P2, P1×P5, P2×P5, P3×P6 and P4×P5 for grain yield/plant; P1×P5, P3×P6 and P4×P5 for shelling percentage. Results showed significant or highly significant heterosis over mid-parents and better parents for all studied traits. The best crosses over mid and better parents were (P1×P5) for number of rows/ear; (P1×P6) for number of grains/row; (P2×P5) for100-grain weight;(P1×P6)for grain yield and (P1×P4) for shelling percentage. The study recommends using inbred line P3 (B73) and crosses P1×P2, P1×P3 and P3×P6 in breeding program of maize to improve the yield and its components where they recorded the highest value of the grain yield/plant and gave a better combining ability.