THE PRESENT work was conducted to study the effects of late planting on the performance of Egyptian cottons, sensitivity to environments and gene action controlled earliness, lint yield/plant, lint % and lint index. A half diallel crosses of eight Egyptian cottons varieties were evaluated under normal and late plantings. The reduction % in lint yield/plant was 23.21 and 23.87% for the parents and F1 hybrids; respectively. The results of stress susceptibility index of LY/P indicated that six parents were tolerant for LY/P to late planting. Sixteen out of the 28 hybrids showed tolerance in LY/P to late planting. The diallel analysis revealed significant (p ≤ 0.01) items; ‘'a'' and ‘'b'', indicating that both additive and dominance effects of genes were involved in the inheritance of the five studied traits. The genetic parameter indicating that ‘'H1'' tended to be more than the additive parameter ‘'D'' under late planting. The regression analysis of Wr/Vr indicated the presence of non-allelic interaction in the inheritance of lint yield/plant under late planting. However, the additive–dominance model was adequate in the inheritance of days to first flower under normal and late plantings. The ‘'b2''' item and KD/KR indicated unequal distribution of dominance and recessive genes in the parents for all traits. The non-additive effects of genes were reflected in the departure of narrow form broad sense heritability. Therefore, pedigree and recurrent selection breeding methods could be effective to isolate lines adapted to late planting.