In this study a complete diallel analysis was done under the condition of nematode infection, using four different parental genotypes of Tomato. Mean squares of the studied genotypes were significant for all studied parameters, which proves the presence of a considerable amount of genetic variation among studied genotypes. Also, GCA and SCA mean squares were highly significant for all studied traits. This means that both GCA and SCA were important in the inheritance of these traits. Likewise, reciprocal effect mean squares were found significant for all the studied traits indicating that these traits are controlled by extra-nuclear factors in addition to the nuclear factors. Also, data showed that significant SCA effects in demand direction for most crosses in some studied traits. The estimations of (σ²g_i) and (σ²s_i) of the parental genotypes for all studied parameters indicated that the genotypes used in this study are of great importance to improve most of the studied traits. The estimation of genetic parameters and heritability for all studied traits proved the predominance of non-additive gene action in the inheritance of these traits. Results revealed that the cross (Cherry x Castle Rock) is a superior hybrid, and it could be selected in the breeding programs to resist nematode. Therefore, using this combination as started material for selection breeding program to produce resistant root-knot nematodes genotypes.