Abstract: In order to understand the genetic variation in pine wood nematode, virulent and avirulent isolates of Bursaphelenchus xylophilus were used as parental isolates to establish crossbred lines, and the virulence and reproductive ability of offsprings were compared with parental isolates. The results showed that hybrid rates were different among different parents, even one pair parents for reciprocal cross. A significant difference was observed in reproductive ability among parental isolates and some crossbred lines on Botrytis cinerea and in masson pine seedlings. The proportion of dead masson pine seedlings inoculating with virulent parent and crossbred lines ranged from 90%-100% after 5 weeks, while only 20% of the seedlings inoculating with avirulent parent showed slight wilting symptons 10 weeks later. Statistical analyses revealed that virulence was positively correlated with propagation rate inside the host pine seedlings in some extent, but was weakly correlated with propagation rate on B. cinerea. Cluster analysis showed that the biological parameters varied between the parents and offsprings, with no kinship bias, suggesting the absence of sex-linked inheritance in virulence and rates of propagation.