The study was undertaken to estimate heterosis and combining ability of new maize inbred lines in F1 combinations for some agronomic traits under two sowing dates for developing superior hybrids. Also this investigation studied the possibility of predicting heterosis and combining ability in maize inbred lines via protein electrophoresis. A half diallel set of crosses involving eight maize inbred lines were evaluated under two different sowing dates and the inbred lines were used for protein electrophoresis study. The obtained data revealed highly significant differences between sowing dates for all studied traits except number of rows per ear. The mean squares due to General Combining Ability (GCA) and Specific Combining Ability (SCA) were significant for all studied traits under both planting dates except 100 kernel weight under late planting date for SCA. GCA/SCA ratios were less than unity for plant height, days to 50% silking, 100 kernel weight and grain yield per plant under normal sowing date and ear height, plant height, number of kernel per row, 100 kernel weight and grain yield per plant under late sowing date and the other traits were more than unity. The hybrids P1xP2, P1xP6, P1xP8, P2xP5, P2xP6, P3xP6, P5xP6, P5xP7 and P6xP7 under normal sowing date and P2xP4, P2xP5, P4xP6 and P5xP6 under late sowing date out yielded the check hybrid. The parental lines P2, P5 and P6 seemed to be the best combiners for grain yield per plant and most of the studied traits under normal and late planting dates. Twenty one out of the twenty eight crosses showed desirable significant SCA effects under normal and late sowing dates for grain yield per plant and most of the other studied traits. The electrophoresis patterns could be useful tools for the identification and characterization of these inbred lines and could be used as biochemical genetic markers associated with hybrid vigor and SCA in maize.