THIS study was accomplished at 2018-2020 seasons at Sakha Experimental Station. Four Egyptian cotton varieties (Giza87, Giza92, Giza93 and Giza96) were used as lines crossed by Pima Early, PimaS-1 and PimaS-6 as testers in line x tester manner. Heterosis and combining ability were determined for yield, its components and fiber traits. Genotypes significantly differed for all traits, Giza96, PimaS-6 and Giza96xPimaS-6 gave highest yield, while Giza87, PimaS-1 and Giza96xPimaS-1 showed the best fiber traits. Giza92 showed the highest positive heterosis for yield and its components when crossed to the three testers, while Pima Early showed the highest positive heterosis for yield and its components when crossed to most of lines. GCA and SCA variances were significant as additive and non-additive gene actions were controlling the studied traits. Giza96 and PimaS-6 were the best combiners for yield and its components, while Giza87 and PimaS-1 were the best combiners for fiber traits. Giza96xPimaS-6 hybrid had the best SCA for yielding traits, while Giza96xPimaS-1 was the best for most fiber traits. Variance of SCA was greater than GCA for almost all traits as non-additive gene action was more important in controlling these traits. Giza96, PimaS-6 and their hybrid were promising for improving the yield potential, while Giza87, PimaS-1 and Giza96xPimaS-1 hybrid were promising for improving fiber quality traits in breeding programs. Giza92, Giza93, Giza96 and Pima Early were the most similar genotypes, whereas Giza87 and the cluster between Giza92 and Giza93 showed the lowest similarity. PimaS-1 and PimaS-6 grouped in one cluster.