Systemic acquired resistance, or simply SAR can spread in plant parts distant from the infection sites due to signal transduction that can be triggered using some elicitors such as ISR2000. The better understanding of the effect of the ISR2000 as an exogenous signal for the activation of SAR has been investigated on tomato plants after challenge inoculations with Potato virus X (PVX). Therefore foliar application of three doses of ISR2000 (R1= 10ml/l, R2=20ml/l and R3=5ml/l) was established in a pot experiment to test their effects on viral disease development in plants infected with PVX inoculated at 72 hours post treatment (hpt). The characters under investigation were measured after 23 days from treatment. The results indicated that, there were some significant differences between the doses of ISR2000 as compared to the control. The dose R2 resulted in the maximum significant increase in plant height with the ratios of 123.88% of the corresponding water control, however the increase in the chlorophyll content after the treatments was not significant. Root total length was significantly increased up to 254.47% due to the R3-treatment. Whereas, all treatments considered having phytotoxic effect compared to the water-control on the leaf areas with a severe decrease up to 79.14% after R3-treatment. Tomato plants inoculated 72 hours after the R1 treatment 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 root total length of the infected plants after the ISR2000-treatments was not significant. Considering the experiment, it can be concluded that, ISR2000 application is improving the ability of the host plant to resist or withstand the attack of the virus and the factory dose 10ml/l is recommended for having better results.