This investigation was conducted during 2014 and 2015 at Kalubia governorate to develop promising hybrids of tomato (Solanum lycopersicum L.) for yield and fruit quality characters under high temperature stress in Egypt using Line x Tester matting design. All studied traits, i.e., fruit set, total yield, marketable yield, average fruit weight, fruit shape index, fruit firmness, number of locules, total soluble solids (TSS%), vitamin C content and titratable acidity have closer values of σ2g and σ2p, meanwhile, the G.C.V. and P.C.V.% which was confirmed by the estimated G.C.V./P.C.V. ratios and high broad sense heritability (BSH) values suggest less effect of environment and the large portion of σ2p was due to the σ2g on these traits, except number of locules and titratable acidity traits which was affected by both genetic and environmental factors. The ratio of σ2GCA / σ2SCA were found less than unity (<1) indicating the preponderance of non additive gene actions over the additive ones for all the studied traits. The prevalence of the non-additive variance suggested heterosis breeding approach is effective way for improvement of these traits. Most of the traits exhibited significant hybrid vigor for some of crosses based on the better-parent. The lines Ent 5 and Ent 17 and the tester TLB 111 showed maximum positive GCA effects for most of the important traits. So, these parents could be successfully used in future for breeding programs. Among all hybrids, Ent 3× 99S-C-39, Ent 5 × 99S-C-39 and Ent 31 × TLB 111 exhibited significant SCA effects for both total and marketable yield characters under heat stress. So, these hybrids could be used in future for breeding to these traits.