Bursaphelenchus xylophilus isolate was inoculated with one-year-old resistant and susceptible seedlings of Pinus thunbergii respectively. The pathological variation in cells and tissues of host were studied. The results showed that pathological symptoms and damages of cells in resistant seedlings were less than those in susceptible ones "for a given inoculation site. Considerable pathological symptoms were firstly seen to a susceptible. And they were mainly distributed on resin ducts in cortex and parenchyma around them. Outermost xylem also appeared the symptoms. However, those symptoms just confined to parenchyma in cortex, resin ducts and parcnchyma around them for a resistant. It was suggested that varied developments of histopathology in pine infected by pine wood nematode were closely related to the resistance of the seedlings.