Five cotton varieties belong to Gossypium barbadense L. i.e. Giza 89,Giza 90 Giza 83, Pima S4 and Pima S6 were selected as parents and crossed in a half diallel pattern to evaluate general and specific combining ability effects (GCA and SCA) and heterotic effects for some agronomic traits i.e. boll weight (B.W.), seed cotton yield (S.C.Y.), lint yield (L.C.Y.), lint percentage (L.%), seed index (SI), length at 2.5% , strength g/tex and micronaire value (Mic). Analysis of variance revealed significant differences among entries for all traits studied except for B.W., S.I. and Mic in F1 and F2 generations as well as length at 2.5% in F2's generation which showed significant differences. The mean squares in both F1's and F2's for general combining ability (GCA) were insignificant for all traits except for S.C.Y. and L.C.Y. in F1's and F2's generations. Meanwhile, the mean squares for specific combining ability (SCA) were insignificant for all traits except S.C.Y. and L.C.Y. in both generations and strength g/tex in F1's generation which showed significant. The GCA/SCA ratio of variance components indicated that additive genetic variance was generally importance for B.W., L%, SI and Mic in the F1 hybrids and for B.W., L.C.Y., L.% and Mic in the F2 generation. Mid-parents heterosis values were significant and positive for S.C.Y., L.C.Y. and length at 2.5% in the cross Giza 89 x Giza 90 (P1 x P2), S.C.Y., L.C.Y., L% and length at 2.5% in the cross Giza 89 x Giza 83 (P1 x P3), S.C.Y., S.I., length at 2.5% and Mic in the cross Giza 89 x Pima S4 (P 1 x P 4), SCY, L.C.Y. and length at 2.5% cross Giza 89 x Pima S6 (P1 x P5), SCY, LY and Mic in the cross Giza 90 x Giza 83 (P2 x P3), S.C.Y., L.C.Y.and length at 2.5% in the cross Giza 90 x Pima S4 (P2 x P4), length and Mic in the cross Giza 83 x Pima S4 (P3 x P4) and S.C.Y. in the cross Pima S4 x Pima S6 (P4 x P5). On the other hand, significant negative heterotic values were observed for B.W. and S.I. in the cross Giza 89 x Giza 90 (P1 x P2), B.W. in the crosses of Giza 89 x Pima S4 (P1 x P4) and Giza 90 x Giza 83 (P2 x P3). Better-parents heterosis values were significant and positive for 1% in the cross Giza 89 x Giza 83 (P1 x P3), S.I. and length cross Giza 89 x Pima S4 (P1 x P4), S.C.Y. in the cross Giza 89 x Pima S6 (P1 x P5), L.C.Y.in the cross Giza 90 x Giza 83 (P2 x P3) and S.C.Y. and L.Y. in the cross Giza 90 x Pima S4 (P2 x P4). These results indicated to the importance of specific combining ability in the genetic expression of these traits with respect to the studied crosses. Regarding inbreeding depression, significant positive effect were obtained for L.C.Y.in the cross (P1 x P2), B.W., S.C.Y. and L.C.Y.in the cross (P1 x P3), S.C.Y .and S.I. in the cross (P1 x P4), S.C.Y., L.Y. and L.% in the cross (P1 x P5), S.C.Y. and L.C.Y. in the cross (P2 x P3), S.C.Y., L.C.Y. and L.% in the cross (P2 x P4), S.C.Y. in the cross (P2 x P5) and in the cross (P3 x P4) and S.C.Y. in the cross (P4 x P5). This finding revealed the importance of heterotic effect in these traits with respect to the studied crosses .