Phenolic compounds in addition to activity of polyphenol oxidase (PPO) and peroxidase (POD) were significantly increased in tomato plants in response to Fusarium oxysporum f.sp. radicislycopersici (FORL) infection, whereas chitinase and β-1,3 glucanase activities were significantly inhibited when compared with the healthy plant. Trichoderma harzianum and chitosan reflected many components of defence signals which leading to the activation of power defence system in tomato against pathogen attack. The reduction in disease incidence and severity was accompanied with remarkable increases in phenolic content and activity of polyphenol oxidase, peroxidase and glucanase in infected plant treated with T. harzianum and chitosan. On the other hand, chitinase activity showed insignificant increase under the application of T. harzianum and chitosan when compared with the infected untreated control. T. harzianum and chitosan treatment as root dipping in combination with chitosan foliar spray was the most effective treatment against Fusarium crown and root rot disease (FCRR) incidence and severity, through induction of physiological host defence mechanisms. Induction of systemic resistance against FORL is one of the main mechanisms by which T. harzianum and chitosan contribute to tomato plants protection.