This investigation was conducted to measure the effects of silkworm diseases on the cocoon crepe. The sample farmers were selected at three areas in Korea. a. Banga Ri, Namsa Myoen, Yongin Kun, Kyoenggi Do b. Moorim Ri, Yakmok Myeon, Chilkok Kun, Kyeongsangbuk Do c. Oero Ri, Buksam Myeon, Chilko Kun, Kyeongsangbuk Do 1. Reduction ratio of crops by the silkworm disease was 5.5% in spring season, and 8.9% in the autumn but 7.2% in a year. Including disease damaged cocoons being spoiled cocoons, it was 8.3%. 2. The ratio of disease-damage by the polyhedrosis virus and flacherie was 17.8% of whole disease at young instar and was 82.2% at advanced instar which showed highest ratio. 3. Average production amount of the cocoon was 27.74kg, The reduction amount by the silkworm disease against the estimated production aomunt was 2.411kg. 4. Reduction of amounts by unknown factors was 3.611 kg. This was 1.5 times of reduction amount by the disease. This nay be chiefly due to the missing silkworms and spoiled cocoons. 5. Ratio of farmers harvesting stable cocoon crops was 54.7% in spring rearing season but 21.9% in autumn. 6. Damage ratio of factors other than the silkworm disease was 10.70% and it was 17.87 % of total mortality.