Abstract: The bacteria carried by different nematodes which were collected and isolated from xylem of infected pine trees of Pinus genus in different areas were identified. The toxicity of culture liquid of these bacteria was tested with seedlings and callus tissue of Pinus nigra. The results indicated that the predominant bacterium species carried by pine wood nematode was Pseudomonas fluorescens, which was different from bacteria species carried by other nematodes. The toxicity of the predominant bacterium carried by pine wood nematode was the most virulent, while toxicity of the bacteria carried by Bursaphelenchus mucronautus and Aphelenchoides sp. nematode were moderately virulent. The bacterium carried by Rhabditida sp. nematode was not toxic. The results farther showed that the bacteria carried by pine wood nematode would play an important role in the pathogenic process.