A Number of 38 single crosses obtained directly from crossing of nine inbred lines in a half diallel system and two checks were evaluated in a randomized complete block design, with four replications, in three locations; i.e., Sal-(ha, Gemmeiza and Sids Res. Stations in 2005 summer season. The objectives of this study were to estimate heterosis and combining ability. The combined analysis of data across environments showed highly significant for locations (Loo), general combining ability (GOA), specific combining ability (SCA) and GCA x Loc. interaction for all studied characters except GCA x Loo interaction for ear height. Additive genetic effects exhibited to have played an important role than the non-additive genetic effects in the expression of all studied characters, except for grain yield under and over the three locations. Also. the additive genetic effects were much more influenced by change of location than the non-additive genetic effects for all studied characters. The highest desirable values of GCA effects were obtained from Sk5170 and Sk8170 inbreds for silking date, plant and ear height. Sk6017, Sk8014 and Sk9195 inbreds for grain yield and ear length and Gm152 inbred for number of rowsfear. The best crosses having desirable values for both SCA and heterotic effects relative to the best check were Sk8012 x Sk8170 for silking date; Sk63 x Sk8012, Sk5170 x Sk8170 and Sl<8014 x Sk9195 for plant and ear height; Sd83 x Sk6017, Sk6017 x Sk8014 and Sk6018 x Sk9195 for grain yield, Sd63 x Sk6017 for ear length and Gm152 x Sk8017 and Gm152 x Sk9195 for number of rowslear. it is worth noting that a cross having good SCA effects, may come from two parents when at least one of them possesses high GCA effects.