The present paper deals with the results of preliminary experiments of the damping-off of pine seedlings (Pinus densiflora and P. thumbergii) in forest nurseries in Shimane Prefecture. Older pine seeds showed poor germinability and heavy occurerce of damping-off comparing with those of the newly collected seeds. Chaetomella, Trichoderma, Alternaria, etc were isolated from pine seeds, and strong pathogenicity was shown with Chaetomella among the fungi isolated from pine seeds. The occurence of pre-emergence and post-emergence damping-off was influenced by temperatures remarkably. Post-emergence damping-off is found in the range of 20_??_30°C, and the highest infection was given at 28°C. Judging from the writers' experiments, post-emergence seems to be more important than pre-emergence for the damping-off of pine seedlings. Fusarium, Trichoderma, Gliocladium and Chaetomella spp. were isolated from diseased pine seedlings in Agenogi-cho, Matsue-City, and Fusarium spp. showed strongest pathogenicity among them. Fusarium fungus grows well in the temperature range of 17_??_30°C and its optimum temperature was at 28°C, and its optimum hydrogenion concentration was lying at pH 5.6. Among Fusarium fungi isolated from the diseased seedlings, Fusarium moniliformae (SHELD.) SNYD. and F. oxysporum (SCHL.) SNYD. et HANS. were proved to be pathogenic to the pine seedlings.