Abstract: The calli of Pinus thunbergii were separately inocul ated under aseptic conditions with aseptic pine wood nematodes[Bursaphelenchu s xylophilus(Steiner & Buhrer)Nickle],bacterium isolate B619 isolated from t he virulent nematode,and mixture of both.It was found that the calli inoculated with the aseptic nematodes or bacterium isolate B619 became browning slightly,w hile those inoculated with the mixture of the aseptic nematodes and bacterium is olate B619 became browning and wilted severly.After inoculating with the mixture of the aseptic nematodes and bacterium isolate B619,the disease index of calli treated with certain antibiotics was lower than that of the control.Those result s further demonstrated that the pine wilt disease was a disease complex involvin g the nematodes and bacteria.Bacterium isolate B619 could hardly propagate in th e calli without nematodes but could quickly propagate in the calli inoculated wi th the mixture of the aseptic nematodes and bacterium isolate B619.This indicate d that the existing of nematodes in the calli was favorable for the propagation of bacterium isolate B619.