Abstract: Two Bursaphelenchus xylophilus isolates (virulent and avirulent) and one B, mucronatus isolate were inoculated separately on 2-year-old seedlings of Pinus thunbergii. The results showed that behavior of nematode dispersal in seedlings caused by different isolates varied considerably, which caused in the development of histopathology within the host to be significantly different. The virulent isolate of B. xylophilus dispersed throughout the host via axial and radial resin duct. Nematodes had a great dispersal ability as the resin duct was a main lacunar system of pine. Population of arivulent isolate of B. xylophilus mainly dispersed into the cortical layer which led to a lower dispersal rate and killing power. Population of B. mucronatus was mainly distributed in the cortical layer and only on few occasions was detected in resin duct. They were nonpathogenicity to pine clue to the low reproduction rate and no virulence to the cell lineages of phloem, vascular cambium, ray in xylem and parenchyma in resin passage. Results also indicated that no nematode dispersal was detected in cambium of pine regardless of the inoculated isolate which was virulent or avirulent. It suggested the cell death of cambium was a bionecrosis and the phenomenon was similar to that of parenchyma cells such as epithelial cell in resin passage, resulted indirectly from nematode dispersal.