Abstract: Three bacterium strains(Njh,NJt and Njw),and two pine wood nematodes(Bursaphelenchus xylophilus and B.mucronatus) were used as inoculum.Both callus and bacteriumfree seedlings of black pine were inoculated with only bacteria,a mixture of bacteria and the aseptic nematodes of Bursaphelenchus xylophilus,a mixture of bacteria and the aseptic nematodes of B.mucronatus,etc.to determine their pathogenicity.It revealed the inoculation only with either aseptic B.xylophilus or B.mucronatus wouldn’t lead to browning of the callus and wilt of aseptic black pine seedlings.But those inoculated with a mixture of the aseptic nematodes and one of the three bacteria mentioned above showed some wilting or browning symptoms.The combination of nematodes with either Njh or Njt caused severe symptoms but the combination of nematodes and Njw weak in symptom.Inoculation with a mixture of B.mucronatus which is weak in pathogenicity and the bacteria also caused serious wilt of pine seedlings and browning of the callus.It indicated that seedling symptoms under artificial inoculation in lab conditions were in a close correlation with the bacteria carried by pine wood nematodes and poorly correlated with species of nematodes.The bacteria carried by pine wood nematodes played an important role in pathogenicity.