Abstract: From 1990～1993,the wirulence of 9 isolates of Bursaphelenchus xylophilusfrom Japan(S-6),Canada(STJ,STW,BxBC)and China and 5 isolates of B.mucronatus from France(Bspfrance),Canada (Q1426),Norway(Norway)and China was tested.Each isolatewas inoculated(1500～2000 nematodes/per seedling)on 3～6-yr-old seedlings of 8 pinespecies through cutting the bark of the stem.As a result,the virulence of B.xylophilus iso-lates is significantly higher than that of B.mucronatus wherever they are from.For each iso-late inoculated,the graph of host mortality of 8 pine species is different even within the samenematode species.The most virulent B.xylophilusn among them,are 5 isolates from China.Isolates from Japan and Canada are moderate while isolates of B.mucronatus are less virulentor avirulent.The result of disease development is related not only to mortality but to meandeath speed(MDS).The MDS is different for different host pines inoculted with the sameisolate and is different for the same pine species inoculted with different isolates as well.Two isolates from China(both from Pinus massoniana in Nanjing and Shenzhen Cities)have asomewhat higher MDS than other isolates.P.massoniana is the most resistant pine afterinoculation while P.thunbergii and P.armandi are the most susceptible.The relationshipamong host,nematode and other factors is also discussed.