This experiment was carried out determine the efficiency of protein and energy utilizations of fattening Korean Native and Holstein breeds and to compare the efficiency of protein and energy utilizations between two breeds. Eight steers were used for metabolism trials and the experimental periods were divided into 5 stages according to body weights from 250 to 550kg. The results obtained were as follow. 1. Although energy utilization and daily body weight gain were not different between breeds, the rate of daily body weight gain of Korean Native Cattle(KNC) decreased after 400kg of body weight while Holstein cattle(Hol) decreased after 450kg of body weight. 2. The nitrogen retention rate was decreased with fattening stage, and the degrees of change were larger in KNC than HOL. 3. Although the amount of nitrogen consumend was not markedly different, the nitrogen retention rate was higher in KNC than in HOL. 4. HOL seemed to have converted feed to body weight gain more efficiently than KNC by 10%.