The effect of the ISR2000 as a plant activator was investigated on tomato plants after challenge inoculations with Potato virus X (PVX). Therefore foliar application of three doses of ISR2000 (R1 = 10 ml/l, R2 = 20 ml/l and R3 = 5 ml/l) was established in a pot experiment to test their effects on growth and physiological parameters in PVX infected plants. The evaluations were made in both inoculated and non-inoculated plants and statistically analyzed in comparison to the healthy (non-infected) water-sprayed control plants. The results indicated that significant reductions in chlorophyll content (66.25%), plant height (66.26%) and leaf areas (45.41%) of non-treated plants were recorded in response to the PVX inoculation. R1 treatments showed the maximum recovery in chlorophyll content (115.97%), plant height (131.63%) and leaf area (126.35%) as compared to non-treated plants. On the other hand, the increase in the total root length of the infected plants after the ISR2000 treatments was not significant. R1 applications promoted chlorophyll content (104.5%) and plant height (121.13%) of the non-inoculated tomato plants but not the leaf areas which decreased to (98.04%) after R1 treatments. This indicates that tomato plants were induced by the ISR2000 after the viral inoculation with more increase in chlorophyll content, plant height and leaf areas than that without the introduction of the virus. Considering the experiment, it can be concluded that ISR2000 application may improve the ability of the host plant to withstand the attack of the virus and the factory dose of 10 ml/l is recommended.