The pea leafminer, Liriomyza huidobrensis(Blanchard), is a widely distributed pest of ornamental and vegetable crops from subtropical to temperate regions and can cause economic losses to host plants by both adult and larval infestations. Larval mining in palisade parenchyma tissue reduces the photosynthetic capacity of plants up to 62%, and severely infested leaves may fall. A further damage to leaves is caused by females, which use the ovipositor to make holes in the surfaces of the leaves promoting the production of leaf exudates on which both females and males feed. The defensive responses of plants to insect herbivory play an important part in the interactive relationship between insects and plants. Insects obtain their nourishment from plants. The nutritional quality of plants and the limited availability of various plant parts deter many insects from using plants as a food source. Insects can be prevented from feeding by plant defenses, ranging from physical barriers to toxins and antifeedants. Plants produce a considerable variety of chemicals with roles in defense against herbivory. These chemicals include secondary plant metabolites and some proteins. Plants can produce proteins that play a critical role in defense by targeting the digestive system of insects, thus impairing the ability of the insect to digest and absorb food. These proteins include protease inhibitors and defensive enzymes which are widespread in plants and are inducible by wounding and herbivory. Four main defensive enzymes, including phenylalanine ammonialyase(PAL), polyphenol oxidase(PPO), peroxidase(POD) and superoxide dismutase(SOD), are key enzymes in the generating process of secondary plant metabolites. However, the interactions between the leafminer and its host plants have been studied mainly on the relationship between host preference of adults and trichomes, volitales, primary and secondary metabolites in host plants. In order to explore the interaction between L. huidobrensis herbivory and plant defense, we investigated the changes in the active levels of these four defensive enzymes in the leaves of cucumber plants that had been continuously feeding by the larvae for 1, 3, 5, 7 and 9 days, respectively.The results indicated that the activities of four enzymes in the leaves of cucumber plants, which had been feeding by the larvae, rose significantly. The magnitude of activity rising of PAL, PPO and POD increased with the increase of damaged levels, i.e. damaged heavily > lightly > systemically > undamaged, but the change of SOD activity were not regular. The maximum activities of PAL, PPO, POD and SOD appeared on the 5th, 1st, 5th and 5th day, respectively, in the systemic controls. They were on the 5th, 9th, 5th and 9th day, respectively, in the damaged-lightly leaves, and on the 7th, 7th, 5th and 5th day, respectively, in the damaged-heavily leaves. The magnitudes of activity increasing of POP and PPO were more than those of PAL and SOD after the leaves had been feeding, which suggests the responses of POP and PPO to insect herbivory are more sensitive than those of PAL and SOD.