Abstract: Pine wilt disease is a very complex disease and has been reported to be caused by pine wood nematode, Bursaphelenchus xylophilus and its accompanying bacteria. However, the role of bacteria in the disease is still debatable. In order to elucidate the hypothesis, we selected one antibacterial agent, oxolinic acid, showing potent antibacterial activity and then evaluated its control efficacy against pine wilt disease in greenhouse and field conditions. Among 6 antibiotics tested, oxolinic acid showed the strongest antibacterial activity against 5 bacteria isolated from three strains of pine wood nematode. In in vivo assay, the agent could effectively suppressed the development of pine wilt disease in 3year old seedlings of Pinus densiflora, it showed 71 % control value when injected 3 mg per seedling. The mixture of oxolinic acid and a nematicidal agent abamectin showed higher disease control efficacy against pine wilt disease than either oxolinic acid or abamectin alone. In addition, oxolinic acid or abamectin alone and their mixture could also controlled pine wilt disease in approximately 20year old pine trees under field conditions. These results strongly indicate that the bacteria accompanying with pine wood nematodes are necessary for the occurrence of pine wilt disease and pine wilt disease could be controlled by antibacterial antibiotic alone and a combination of antibacterial and nematicidal agents.