This experiment was carried out to investigate the effect of energy and protein levels during the lactation period on milk yield. milk composition and body weight of dam in Korean native cows. In this experiment, thirty six heads of nursing cows and calves were allotted to a 3×3 factorial design with three net energy levels (80, 100. 120% of NRC) and three crude protein levels (80. 100, 120% of NRC) from calving to weaning for 180 days. The results obtained from this experiment arc summarized as follows; 1. Dam`s body weight for 180 days was changed with a highly significant difference (P$lt;0.01) from 27.l㎏ increase of the NE 120%-CP 100 to 65.6㎏ decrease of the NE 80%-CP 100%. 2. The average daily milk yield of nursing, cows with 10-day intervals for 180 days did not show a significant difference, although the difference was 0.93㎏ from 3.11㎏ of the NE 100%-CP 120% to 4.04㎏ of the NE 120%-CP 120% (average 3.50㎏). 3. The maximum of average daily milk yield with 10-day intervals for 180 days was 4.76 to 5.36㎏ (average 5.04㎏) without a significant difference by post- partum NE -CP levels. But the lactation day for the maximum of average daily milk yield was changed with a significant difference (P$lt;0.05) from 7.5 days of the NE 80%-CP 120% to 37.5 days of the NE 80%-CP 100% (average 17.8 days). 4. The decrease rate per week and the decrease quantity per day of average daily milk yield for 180 days was 2.22 to 3.30% (average 2.68%) and 15.1 to 21.4g(average 18.1g), respectively. without .1 significant difference by post-partum NE-CP levels. 5. The physico-chemical properities and constituents of milk were not significantly different by treatments, and the energy value of milk per kg was 790 to 850㎉ (average 811 ㎉). 6. In the nutrient levels for the cows during the nursing period, energy levels affected only the body weight of dam with a highly significant difference (P $lt;0.01). However, protein levels did not affect all factors.