Abstract: The activities of Polyphenoloxidase (PPO), Phenylalanine Ammonia Lyase ( PAL), Peroxidase (POD), Superoxide dismutase (SOD) and Catalase (CAT) in ‘Ya’ pear fruit inoculated with Botryosphaeria berengriana f.sp. piricola and sound pear fruit in growth and storage periods were studied. The results show that compared with the uninoculated pear fruit, the PPO activity of the pear fruit inoculated by the pathogen markedly increase in 48 hours after the inoculating treatment, the PAL activity is on the rise during the 120 hours after inoculation, POD and CAT activities reach a peak at 72h after inoculation, and the SOD activity of the inoculated treatment is also obviously higher than that of the contrast, which suggests that those enzymes are closely-related to pear fruit against Botryosphaeria berengriana f.sp. piricola infection. The main defense enzymes at the young stage of pear fruit are PPO, POD, PAL and CAT, which activities are higher at 25～75 d after blossom, and lower from then on; The main defense enzymes with high activity at the premature stage of pear fruit are SOD and PAL. In addition, the activity of SOD heightens sharply at 75 d after blossom, peaks at mature stage of fruit. And the activity of PAL appears a little peak at 115 d after blossom. The activities of these enzymes all declines during storage period, and the ability to resist the growth of pathogen reduces sharply. The disease resistance of pear fruit during different periods concerns the defense enzymes activity very nearly.