The experiments were carried out to investigate the effect of humidity on the cocoon quality, and 4, 000 lots of cocoon pruduced fot five years in Chin yang, Ha dong, Keo chang, San chung of Kyeong nam, and Sun san, Sang ju, Young poong, An dong of Kyeong buk were analyzed. The results were summarized as follows ; 1. The reelability ration, the bave length, and raw silk ration were decreased with increasing the humidity in mounting time, and it was remarkably observed when the relative humidity was over 80%. 2. With increasing the reelability ration, the bave length, and raw silk ration were increased, and the longer the bave lenger the bave length was the higher raw silk ration obtained. 3. The average reelability ration for five years in autumn-rearing period was higher than that in spring-rearing period, but the bave length and raw silk ratio was on the contrary from the above. 4. The reelability ration of cocoon produced in the mountainous area was higher than that in the field area but the shorter the bave length, the raw silk ration had no significant difference between those.