In this study، the effect of salicylic acid (SA) on root knot nematode (Meloidogyne javanica) pathogenicity and induction of some defense mechanisms such as polyphenol oxidase enzyme activity and total phenol accumulation were investigated in greenhouse conditions. We demonstrated that application of 5mM salicylic acid through foliar spray could induce resistance against M. javanica in tomato. Polyphenol oxidase activity and levels of phenol compounds were determined on 1 to 8 days after inoculation. Salicylic acid caused increasing polyphenol oxidase activity that reached maximum level 4 days after nematode inoculation. The highest level of phenolic compounds was observed 4 days after Salicylic acid and nematode inoculation. Also، application of Salicylic acid could decrease the severity of disease in greenhouse. In iddition، in vitro assay showed that salicylic acid increased the death percentage of second stage juvenile (J2). The results showed the induced resistance observed in tomato against M. javanica via application of Salicylic acid، because SA increased the activity of polyphenol oxidase and levels of phenol compounds.