To confirm the effects of wood-inhabiting fungi on the number of pine wood nematodes (Bursaphelenchus xylophilus) carried by the Japanese pine sawyer (Monochamus alternatus), we attempted to change the mycoflora and also to prevent blue-stain fungi, the main food source fungi of the nematodes, from spreading throughout pine wilt-killed Pinus densiflora wood by inoculating 12 other fungi into the dead logs. Trichoderma sp. 2, Trichoderma sp. 3, and Verticillium sp. inoculation treatments tended to decrease the number of the nematodes carried by the beetles. These fungi were more or less antagonistic to the blue-stain fungus Ophiostoma minus, and Trichoderma sp. 2 and Trichoderma sp. 3 grew faster than O. minus on four kinds of media.