This research was conducted at the Department of Maize in the General Commission of Science Agriculture Research (GCSAR) Damascus, Syria. The genetic material included parental inbred lines and the first and second (F1, F2) generations of two hybrids of maize to estimate the heterosis, degree of dominance and the inbreeding depression under two treatments of irrigation. Results showed that mean squares of inbred lines P1, P2 and the first generation were non significant for all studied traits, while the variance of the second generation F2 was highly significant under the stress and non stress treatments, The hybrid (IL.275–6×IL.362–6) showed the highest average of yield under stress and non stress treatment, a Positive heterosis effect relative to mid parents and the better parent was recorded for ear height, ear diameter, 100 kernels weight and yield per plant, The degree of dominance showed that the branches per tassel was controlled by partial dominance on the other hand the ear diameter and yield per plant showed the greatest values of inbreeding depression, Results revealed the effective selection among the F2 individuals of the studied hybrids specially the hybrid (IL.275–6× IL.362–6) through the late generations (S5, S6) to get new inbred lines of maize which had dominance desirable alleles to improve yield and it's components especially under water stress conditions.