Fusarium oxysporum f. sp. lycopersici (Fol), the causal agent of vascular wilt, is one of the limiting factors of production of tomato. Study on the biocontrol mechanisms of antagonist agents, especially induction of resistance in the plant, received a great deal of attention because of the undesirable effects of agrochemicals on human health and environment, and the inadequacy of other disease management methods. In this study the biocontrol activity of Th-14 and Ta-30 isolates (Trichoderma harzianum and Trichoderma atroviride, respectively) against Fol was evaluated by split-root method in greenhouse. In this experiment, six-leafed seedlings of Early Urbana Y cultivar were used. The activity of phenylalanine ammonialyase,polyphenol axidase and peroxidase was measured on 0, 7, 11, 14, 17 and 21 days after Fol inoculation, to assess the ability of antagonist isolates to induce defense responses in the tomato plant. This experiment was performed in a completely randomized factorial design in four replications. The results showed that in the seedlings treated with Trichoderma isolates and Fol, increased the activity of phenylalanine ammonialyase, polyphenol axidase and peroxidase significantly (p≤0.05), in addition to significant reduction (p≤0.05) of the mean values of disease severity and incidence compared with control. It was also found that the combined application of isolates compared to separate treatments was more effective in increasing the level of activity of enzymes. Since Th-14 and Ta-30 isolates were able to induce changes in the activity of phenylalanine ammonialyase, polyphenol oxidase and peroxidase enzymes and reducing the severity of the disease, the use of these isolates can be promising in stimulating indction of resistance and controlling Fusarium wilt disease in tomato