Hayman's diallel cross analysis was employed to investigate the nature of genetic system controlling some earliness characters in nine Egyptian cotton varieties and their half diallel crosses. The information obtained with regard to D and H1 suggested that in all traits, additive part of the genetic variance was more important than dominance con‌cerning gene distribution, and all traits expressed unequal gene distribu‌tion. Most of dominant genes had negative effects in all characters ex‌cept days to first flower in F2 generation. Dominance degree was over dominance for all traits except days to first flower in F1, which exhibited complete dominance and position of first fruiting node in F1. The narrow sense heritability values of more than 0.50 were de‌termined for all traits in Fl generation. However, in F2, generation, it was 0.12, 0.38 and 0.33 for days to first flower, position of first fruiting node and days to boll opening , respectively. For all traits in F1, the Wr/Vr regression coefficients were not sig‌nificantly different from unit slope, indicating additive gene action with partial dominance. In F2, the Wr/Vr regression coefficients were not sig‌nificantly different from unit. The results reached from the distribution of parents along and/or around the regression line suggested that Giza 83 was best parent for breeding program for earliness trait.