Abstract: Jiashi and 86-1 muskmelon fruits were used as the materials to investigate the relationship between the difference of the resistance capacity and the reactive oxygen species (ROS) related metabolism in muskmelon fruit inoculated with Alternaria alternata. Six holes were made on the equatorial part of fruit at the same distance and inoculated with 20 μL A. alternata, and stored at 7℃. The changes of disease spot diameter, superoxide anion, the content of hydrogen peroxide, malondialdehyde (MDA), as well as ROS related metabolism enzyme such as polyphenol oxidase, peroxidase, superoxide dismutase and catalase were determined at regular intervals. The results indicated that the lesion diameter of 81-6 melon peel and pulp was larger than that of Jiashi melon, and the diameter of both melon lesions was bigger than that of peel. After A. alternata infecting the fruit, early induction of ROS rapidly accumulated, promoted enzyme activity, and reduced the content of MDA. The levels of ROS accumulation and enzyme acuities in Jiashi muskmelon were higher than the corresponding 86-1 muskmelon;moreover, the activities of ROS and enzyme activities of both melon skins were higher than those of pulp, but the content of MDA was the opposite. In conclusion, the postharvest disease resistance of melon fruit was closely related to the metabolism of ROS. Jiashi muskmelon's disease resistance was stronger than 86-1 muskmelon and the disease resistance ability in pericarp was stronger than that in sarcocarp.