The phenylpropanoid pathway is an important pathway in secondary plant metabolism that produces a variety of phenolics with structural and defense-related functions including lignins, phenolic acids, stilbenes, and flavonoids. Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) is a key enzyme in the first step of the phenylpropanoid pathway, which is directly involved in the synthesis of phenols, phytoalexins, and lignin that are associated with the localized resistance processes (Ryals et al.,1996). Polyphenol oxidase (PPO; EC 1.10.3.1) and peroxidase (POD; EC 1.11.1.7) are both involved in lignification of host plant cells and considered as key enzymes related to defense reaction against pathogen infections (Mayer and Harel, 1991; Wallace and Fry, 1999). The results showed that chitosan or methyl jasmonate treatments induced enzyme activity of tomato compared with the control. However, 0.1% chitosan and 500 ml/l methyl jasmonate induced more enzyme activity compared with the control and chitosan or methyl jasmonate alone. Chitosan or methyl jasmonate treatment induced the activities of defenserelated enzymes and then promoted protection of some fruits and vegetables. The results suggested that the increased activities of PAL, POD and PPO in tomato induced by 0.1% chitosan and 500 ml/l methyl jasmonate might possibly be of benefit to disease resistance during storage as well. The cause of the different enzyme activity of tomato between chitosan or methyl jasmonate alone and chitosan combinated with methyl jasmonate was still not clear.