The performance response when lactating cows were fed high level feeding of corn silage. as a only roughage, were studied in reprications of a 3×3 Latin square design, each treatment represents 3 cows. The 9 cows from 3 treatments that is 3 different corn silage levels were fed for 16 day`s main experiment period following 10 day`s preliminary period. The corn silage feeding levels were. (A) Basal ration with corn silage of 3% of body weight, (B) Basal ration with corn silage of 8% of body weight. (C) Basal ration with corn silage of 10% of body weight. The result of this study shoved a summary as follows. 1. There was no significant difference among 3 different levels of corn silage feeding in milk production. The production index was 100 for treatment A. 87 for treatment B and 90 for treatment C. However, there was a lute difference in butter fat content with the index of 100 for treatment A. 99 for B and 95.5 for C respectively. 2. In body weight change, There was no difference among 3 treatments, but slight difference occurred between B and C treatments without statistical significance. 3. The ketone body contents in urine was tested, there was no significant level was founded by feeding of high level of corn silage for lactating dairy cows.