Abstract: The dynamic changes of superoxide anion O2-, hydrogen peroxide (H202), superoxide dismutase (SOD), eatalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and malondialdehyde (MDA) in the barks of resistant and susceptible poplar cultivars, Populus tomentosa and P. beijingensis infected with Botryosphaeria dothidea, were measured, and the generation of reactive oxygen species (ROS) in the interaction between poplar cuhivars and Botryosphaeria pathogen, the activity change rule of oxidation enzyme-resistance and their relationship with the disease resistance of testing poplars were also analyzed in the paper. The results showed that the content of O2-and H2O2in bolh poplar cuhivars increased with the time after inoculation. The "oxidative burst" was clear in resistant cultivar and unclear in susceptible one; POD activity increased with a higher level in resistant cultivar than that in the susceptible one at the late stage; SOD and CAT activities increased at first stage and declined later, while the inhibition was more significant io the susceptible one; APX activity changed a lot in two cultivars and variable range was significant in the resistant one. The increased MDA appeared that "oxidative burst" was likely to initiate membrane lipid peroxidation. MDA content has a sharp increase in testing P. beijingensis at late stage after inoculation and a significant positive correlation with the rate of O2: generation.