The present study was carried out at Seds Agricultural Research Station, Cotton Research Institute, Agricultural Research Center, Egypt, during 2019 and 2020 seasons. This investigation was carried out to estimate heterosis, combining ability, proportional contributions, genetic components and heritability estimates of some characters for six Egyptian cotton varieties as lines i.e, Giza 80, Giza 86, Giza 90, Giza 93, Giza 94 and Giza 95, while, the other three genotypes used as testers were Karshenky, Ustraly 13 and Pima S4, using line x tester analysis. In 2020 season a randomized complete block design with three replications was carried to evaluate all genotype (nine parents and their 18 F1s crosses) for some genetic parameters. The results indicated that mean squares due to the genotypes, parents, parents vs. crosses, crosses, lines, testers and Line x Tester were highly significant for all studied traits, except boll weight, seed index and lint index at tester and fiber strength for Line x Tester. The following crosses demonstrated the best heterosis relative to mid- and better-parent, i.e, Giza 80 x Karashenky, Giza 86 x Ustraly 13 and Giza 86 x Pima S4 for most yield studied traits and the crosses Giza 93 x Karashenky and Giza 93 x Ustraly 13 for most fiber quality traits. The results revealed that the lines Giza 86 and Giza 94 were significant and positive desirable GCA effects for most yield traits. Giza 93 had significant desirable GCA effects for all fiber traits, in this respect, the results of testers showed that Pima S4 had significant desirable for some yield and fiber traits. However, estimates of specific combining ability (SCA) effects for crosses Giza 86 x Ustraly 13, Giza 90 x Pima S4, Giza 93 x Karshenky and Giza 95 x Pima S4 were significant desirable SCA effects for most yield traits, while, the crosses Giza 90 x Pima S4, Giza 93 x Karshenky and Giza 95 x Pima S4 were significant desirable SCA effects for most fiber traits. The results showed that proportion contribution of lines was higher than of lines x tester interaction contribution and testers for all studied traits. The non-additive of genetic parameters was larger than additive genetic variance with respect to all studied traits except lint percentage, seed index, lint index and upper half mean. The highest broad sense heritability estimates was observed in case of UHM with values of 88.47% and the lowest was for fiber strength with value of 32.24%, while for narrow sense heritability, it was ranged from 8.04% to 49.03% for boll weight and upper half mean, respectively. Generally, Giza 86 and Giza 94 could be used in breeding programs for improving high yielding varieties, while Giza 93 could be considered as excellent parent for breeding programs to produce new varieties characterized with best fiber properties.