<p>The diallel analysis provides basic genetic information that is critically important to identify parents which can be involved in hybridization breeding programs. Five tomato inbred lines and 10 F₁ hybrids produced by crossing of them in half diallel fashion excluding the reciprocals were evaluated to estimate the magnitude of heterosis for late blight resistance. The combined analysis from a two-year field experiment revealed that there was a significant effect of tomato genotype (hybrids and lines) for all traits related to disease intensity. The cross-combination Roma VF × Eshete, ARP tomato d2 × Eshete, Melkashola × Bishola and Bishola × Eshete showed negative higher parent heterosis (HPH) for all disease variables. Melkashola × ARP tomato d2 showed negative highly significant higher parent heterosis (HPH) for AUDPC for severity (leaf infection) and infected leaves (%). Negative and significant higher parent heterosis were recorded by four crosses out of ten crosses for all studied characters indicating the crosses were exhibiting in desired direction for late blight resistance improvement. Melkashola × ARP tomato d2 showed negative highly significant higher parent heterosis (HPH) for AUDPC for severity (leaf infection) and disease incidence on leaves. Thus, heterotic breeding for tomato late blight resistance improvement through utilizing the potentiality of this parents is feasible. The cross Roma VF × Bishola showed negative highly higher parent heterosis (HPH) for AUDPC for severity (leaf infection), as well as disease incidence on leaves and fruits. The information generated by this study can be useful for tomato breeding programmes aiming to improve resistance to late blight.</p>