【Objective】 To isolate the pathogenic bacteria of Drosophila suzukii and study the mechanism of bacterial pathogenicity towards the host. 【Methods】 The pathogenic bacteria were isolated by the plate streaking method and identified based on the 16S rRNA gene sequences. The acidified ethanol method was employed to measure the ability of the isolate to cause browning. The pathogenicity of the isolate was examined by oral infection. Dihydroethidium (DHE) was used to determine the level of reactive oxygen species (ROS), and brilliant blue staining was used to examine the intestinal permeability. 【Results】 A strain was isolated from the brown culture medium of D. suzukii and identified as Gluconobacter oxydans. The strain reduced the survival rate of D. suzukii to 49.41% on day 8 (P<0.001). Furthermore, it weakened the tolerance of D. suzukii to desiccation and starvation, reducing the survival rate to 58% and 50.9% at the time points of 24 h and 32 h, respectively (P<0.001). Moreover, the flies treated with G. oxydans displayed impaired integrity of the intestine and had higher level of ROS in the guts than the control group (P<0.001). G. oxydans robustly reduced the medium pH (pH 2.0), which compromised the survival rate of D. suzukii and the growth of Lactobacillus plantarum, a probiotic of D. suzukii. 【Conclusion】 G. oxydans was a potent pathogen capable of reducing the survival rate of D. suzukii by lowering the medium pH and inhibiting the growth of probiotics, demonstrating the potential of serving the biocontrol of D. suzukii.