In this study six Egyptian cotton varieties were used. These varieties were; Giza 80 (p₁), Giza 83 (p₂), Giza 85 (p₃), Giza 88 (p₄), Giza 90 (p₅) and Giza 45 (p₆). All six varieties are belonging to the species Gossypium barbadense L.              The genetic materials used in the investigation included six cotton varieties and their 15 F₁ hybrids. In 2008 growing season, these genotypes were evaluated in Cotton Research Experimental at El-Minia Governorate. Heterosis, gene action, general and specific combining ability and heritability in broad and narrow senses were estimated, yield component traits and fiber properties; seed cotton yield /plant, lint yield /plant, boll weight, number of bolls /plant, seed index, lint percentage, fiber fineness, fiber strength, fiber length and uniformity ratio.            The results showed that the mean performances of most the 15 crosses were better than their both parents. The mean squares of genotypes and crosses were significant or highly significant for all studied traits. The results also cleared that the variety Giza 83 (p₂) was the highest yielding parent for seed cotton yield /plant, number of bolls /plant and lint percentage. The parental variety Giza 85 (p₃) exhibited the best mean performances for lint yield /plant, boll weight and seed index, and the parental variety Giza 45 (p₆) showed the best mean performances for all fiber properties. Therefore, these parental varieties could be utilized in a breeding program to improve these traits through the selection in segregating generations.             Heterosis over the mid-parents and better-parent, the results showed that the cross (p₁×p₅) was highly significant and positive for seed cotton yield /plant (S.C.Y. /P.), lint yield /plant (L.Y. /P.) and number of bolls /plant (N.B. /P.) and the cross (p₁×p₆) had the highest significant values and positive for fiber fineness (F.F.) relative to the better-parent and fiber length relative to the mid-parents.            From the analysis of diallel crosses, the variety Giza 45 (p₆) was the best combiner for number of bolls /plant (N.B. /P.), fiber strength (F.S.), fiber length (F.L.) and uniformity ratio (U.R.). While, the variety Giza 83 (p₂) was the best combiner for seed cotton yield /plant (S.C.Y. /P.), lint yield /plant (L.Y. /P.) and lint percentage (L. %) and Giza 85 (p₃) was the best combiner for boll weight (B.W.) and seed index (S.I.).           The results also showed that the four crosses; (p₁×p₅), (p₂×p₅), (p₂×p₆) and (p₃×p₆) were positive and highly significant specific combining ability effects values for seed cotton yield /plant (S.C.Y. /P.), lint yield /plant (L.Y. /P.), boll weight (B.W.) and number of bolls /plant (N.B. /P.), and cross (p₂×p₄) for lint percentage (L. %). Concerning fiber quality properties, the two crosses (p₁×p₆) and (p₂×p₄) showed desirable highly significant specific combining ability effects values for all fiber properties under study.           The results revealed that the magnitudes of non additive genetic variance including, dominance (s² D) were positive and larger than those of additive genetic variance (s² A), for seed cotton yield /plant (S.C.Y. /P.), lint yield /plant (L.Y. /P.) and number of bolls /plant (N.B. /P.). On the other hand, the results revealed that the magnitudes of additive genetic variance (s²A) were positive and larger than those of dominance genetic variance (s²D), for lint percentage (L. %), fiber fineness (F.F.), fiber length (F.L.) and uniformity ratio (U.R.).          The estimated heritability values in broad sense (h² b.s %) were larger than their corresponding heritability values in narrow sense (h² n.s %) for all studied traits. The calculated values in broad sense ranged from 53.71 % to 95.23 % for seed index and lint percentage, respectively. Narrow sense (h² n.s %) ranged from 9.43 % to 63.19 % for boll weight (B.W.) and fiber length (F.L.), respectively.