[Aim] Mikania micrantha is one of the most dangerous invasive weeds in the world, which has caused serious damage to the environment, agriculture and forestry in China. Pachypeltis sp. is a potentially important natural enemy for M. micrantha management. This research aimed for investigating the effects of Pachypeltis sp. feeding on the defense-related enzymes, nutrition and chlorophyll in M. micrantha leaves, which would provide a basis for the management of M. micrantha using the natural enemy Pachypeltis sp.[Method] The local natural enemy Pachypeltis sp. was collected from the field in Ruili City, Yunnan Province, China and was fed with M. micrantha. The activities of peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD), and the contents of soluble sugar, soluble protein and chlorophyll of M. micrantha leaves were determined after 12 h, 24 h, 48 h and 96 h exposure to the mirid; plants not exposed to Pachypeltis sp. served as control.[Result] Compared with the control, the activities of POD and CAT increased and SOD activity decreased in the leaves of M. micrantha after fed by Pachypeltis sp. for 12 h. Afterwards, the activities of POD and SOD increased while CAT activity decreased. The activities of POD and SOD reached the highest values while that of CAT was the lowest at 48 h. The activities of POD and SOD declined after 96 h herbivore exposure, but were still higher than those in the control. CAT activity at 96 h was similar to that at 48 h. After feeding by Pachypeltis sp., the amount of soluble sugar in M. micrantha leaves increased significantly with the highest value at 96 h. The amounts of soluble protein and chlorophyll decreased significantly and reached the lowest values 39.30% and 69.94% lower than the control, respectively, after 96 h exposure to the herbivore.[Conclusion] The natural enemy Pachypeltis sp. would severely damage the normal physiological functions in M. micrantha leaves, causing wilting and gangrene.