Maize (Zea mays L.) is one of the most important cereal crops cultivated globally leading total yield production of crops. The national average maize yield in Ethiopia is low. The development of inbred lines and hybrids is among the widely used breeding strategies in maize. Choice of promising germplasm with good combining ability and heterosis is very important to develop high yielding maize varieties Hence, this study was carried out with the objectives to determine general combining ability of lines and specific combining ability of their crosses for grain yield and other agronomic characters, to estimate standard heterosis and identify crosses with higher yield than the standard hybrids. Thirty crosses (fifteen inbred lines each crossed with two testers) along with three popular standard hybrids were evaluated in alpha lattice design with two replications during the 2018 cropping season at Adet. There was significant difference among genotypes for all the traits except number of kernel per row (NKR) and ear length (EL). Mean squares for GCA of lines were significantly different at 1 % and 5 % probability levels for all evaluated traits, whereas SCA mean square was significantly different at 5% probability only for days to maturity (DM), ear height (EH), harvest index (HI) and thousand kernel weight (TKWT). Out of all inbred lines, L4 was the best combiner followed by L11 for grain yield with the general combining ability (GCA) effects of 2867.73 and 488.70 respectively, whereas L11 x T2 the best cross for grain yield with the specific combining ability (SCA) of 1035.67. Percentages of standard heterosis in each trait were observed from negative to positive values. The highest estimate of standard heterosis for grain yield was observed in L4 x T2 (40.32%, 12.13% and 43.61%) followed by L4 x T1 (40.30%, 12.12% and 43.60%) and L11 x T2 (24.95%, -0.15% and 27. 89%) over the standard checks BH 540, BH 660 and AMH 851, respectively. Based on mean grain yield, standard heterosis and combining ability L4 x T1, L4 xT2 and L11 x T2 are promising crosses that could be promoted for further use in maize breeding program after additional verification of the results. Key words: Combining ability, Inbred lines, Standard heterosis and Maize