Combining ability information is necessary for selection of suitable advanced lines for hybridization and identification of promising hybrids for development of improved varieties. A number of 14 maize (Zea mays L.) inbred lines and 91 related crosses were evaluated over two years, 2008 and 2009, in a temperate-zone of Iran. The objectives of the study were to identify the best general and specific combiners, heterosis and type of gene actions responsible for agronomic traits. Except for grain yield and growing degree day to milky, significant general (GCA) and specific (SCA) combining ability were observed for all traits. The Baker ratio for plant height (0.15), ear height (0.26), growing degree day to milky stage (0.04), and grain yield (0.002) showed the predominance of non-additive gene effects in the expression of these traits. The heterosis observed for grain yield, grain number, pollination period, ear and plant height was considerably higher than that observed for other traits. The correlations (r) of $F_1$ means and SCA effects were positive and significantly higher than that of r ($F_1$, mid-parents) and r ($F_1$, heterosis) for all the traits except cob percent, growing degree days to silking, and physiological maturity. MO17, K3547/5, and K3615/2 had negative GCA effects for growing degree day to milky stage and maturity. Among hybrids, MO17 ${ imes}$ K3653/2, B73 ${ imes}$ K3651/2, and K3545/6 ${ imes}$ K3493/1 with positive SCAs for pollination period and grain yield had also negative SCA effects for degree day to silking and milky stages. Therefore, the use of these inbred lines and hybrids increases the response to selection for increasing grain yield and early maturity in maize.