The present study aimed to asses the genetic evaluation of 5 genotypes and their 10 crosses for heat tolerance, as well as to determine the genetic behavior of  heat tolerance related criteria under heat stress condition in tomato in five tomato genotypes (five parents, [P1 (s.60), P2 (HE.15.4.1), P3 (D.7.4.1), P4 (KL.3), P5 (KL.5)], and their ten F₁ hybrids) during summer season of 2014and2015 at The Experimental Farm At El-Kassasien, Hort. Res. Station, Ismalia, Egypt and data were analyzed by half diallel analysis. Seven characters were studied ,osmotic pressure (OP), pollen fertility (PF), 50% flowering, fruit setting (FS), fruit weight (FW), total yield (TY), and total soluble solid (TSS). Positive heterosis in OP, PF, TY, FS and TSS for almost all hybrids, except (3×5) (4×5) hybrids was observed which possessed a negative heterosis in FS; Negative heterosis in 50% F, and FW for almost all hybrids, was detected except (1×4) (4×5) hybrids which possessed a positive heterosis in FW. High significant differences of additive effect (D) estimates was obtained for all studied characters expect FS. Mean degree of dominance (H₁/D)^0.5 indicated the presence of over dominance for TY, FW, PF, while the  other characters,OP, 50% F, FS and TSS showed partial dominance. The deviation of b-value from zero was significant for TY, FW, 50% F, PF and FS suggesting the absence of non-allelic interaction, while it was insignificant for TSS and OP suggesting the presence of non-allelic interactions. High heritability (h²_b) from (0.86-0.98) was obtained for all characters, indicating the little influence of the environmental conditions and subsequently, these character considered as high inherited ones. (h²_n) from (0.32-0.96) was obtained for all characters.