Abstract: A half-diallel set of crosses was established among six local cultivars of cotton namely Giza-88, Giza-90, Giza-87, Giza-89, Giza-91 and Giza-83 in order to estimate the genetic parameters of agro-physiological traits under two contrasting environments of a clay-fertile soil and a sandy-calcareous infertile soil. The results revealed that the additive and non-additive gene effects were involved in the control of the studied traits in both environments. Most of the variation was attributed to the non –additive gene. Drought stress reverse the gene effects controlling the plant height and number of opened boll under favorable environment, whereas the additive gene effects were more important in favorable conditions but under stress the dominant effects of the genes were more important. The Wr/Vr analysis revealed that over-dominance was operating for the F1 generation and partial dominance was detected for the F2 generation under the two environments. The order of the dominance of the cultivars Giza-87 and Giza-89 were reversed under drought. The genetic parameters indicating non-equal distribution of dominant and recessive alleles among the six parents analyzed. Narrow-sense heritability values were much smaller relatively to broad-sense heritability in the two environments except for the plant height indicating that the additive component was smaller than the other components of variance.