Genetic distance (GD) among six maize inbred lines was determined based on the ISSR markers. A total of 96 amplification bands were produced by ten ISSR primers; 35 out of them were polymorphic (36.46 % polymorphism). Highest similarity level (94.3%) was between P2 and P3 that are closely related. Highest genetic diversity was between P1 and P4. Inheritance of earliness, grain yield and its components in three specific crosses (P2 x P3 low diversity, P5 x P6 moderate diversity and P1 x P4 high diversity) were studied in a trial consisting of 6 populations (P1, P2, F1, F2, Bc1 and Bc2) during 2013 and 2014 years. Inbred line differences occurred regarding genetic background, genetic variance within F2 population, desirable heterosis and inbreeding depression were detected for all studied traits in the three crosses. Potence ratios were higher than unity indicating over-dominance towards the desirable parent. Additive gene effects (a) and dominance gene effects (d) were significant for most studied traits. High heritability in broad-sense was detected, except for grain yield plant -1 in cross No.1. Heritability in narrow-sense was low. Variance in F2, mean performance in F1 and GCV% increased with increasing GD in the cross P1xP4 followed by cross P5xP6 and then by cross P2xP3. Values of r were 0.98** between GD and variance of F2, 0.97**between GD and mean performance of F1 and 0.79** between GD and GCV% for grain yield plant -1 . Hence,ISSR markers method proved powerful, reliable, fast and inexpensive for screening genetic diversity between maize inbred lines.