Abstract: Eighteen bacterial strains belonging to Pseudomonas, Pantoea and other genera, which had been isolated directly from pine wood nematodes(PWN) in the infected wood of Pinus thugbergii and P.massoniana, and had been identified, were studied in our research. This diseased wood was collected from several disease stages of two main pine species in six epidemic provinces. To obtain aseptic PWN, the septic eggs were treated with 30% H₂O₂ and the observations of effects of PWN with bacteria on the reproduction of PWN were carried out under axenic conditions. The results indicated that only bacterial strains in Pseudomonas promoted the propagation of PWN, while all the other strains showed inhibitory effects. The experiment showed that the bacterial strains of Pseudomonas played very important roles in the development of pine wilt disease. Our findings provide further experimental evidence for the hypothesis that pine wilt disease is a disease complex resulted from infection by both PWN and the bacteria they carrying.