A series of experiment was undertaken (1) to investigate the growing and fattening performances of Korean native young bulls, (2) to find out the statistical relationships between nutrients intake and increase in body weights, (3) to determine the requirements of DM, TDN and DCP, and (4) estimate the requirements of DE and ME of Korean native young bulls. The experiment was conducted from Aug. 1, 1971 to Apr. 27, 1972 with a total of 30 heads of Korean native young bulls. The experimental rations consisted of 3 levels of TDN (80, 100, 120%) and 2 levels of DCP (90, 100%) based on the requirements of beef cattle in NRC (1970) as follows T₁ : DCP 100%, TDN 80% ; T₂ : DCP 100%, TDN 100% ; T₃ : DCP 100%, TDN 120% ; T₄ : DCP 90%, TDN 80% ; T_5 : DCP 90%, TDN 100% ; T_6 : DCP 90%, TDN 120%. The results obtained are summarized as follows: 1. Total and daily body weight gains were significantly (P$lt;0.01) affected by the levels of TDN, however, the effect of DCP levels was insignificant. It was found that the average daily gain was increased as the level of TDN in ration was increased, Average daily gain of T₁, T₂, T₃, T₄, T_5 and T_6 for period 1, period 2 and period 3 were 0.66, 0.89, 0.78; 1.01, 0.96, 0.87; 1.17, 1.08, 0.89; 0.69, 1.96, 0.77 ; 0.97, 0.93, 0.89; and 1.08, 1.06, 0.94㎏, respectively. Generally average daily gains during the last stage of fattening period were somewhat lower than early period of fattening. 2. The growth patters of the Korean native bulls were precisely fitted by the linear regression equation with highly significant (P$lt;0.01) correlation coefficients as follows; T₁: Y=24.31X-48.67 (r=0.998**) T₂: Y=28.43X-76.91 (r=0. 998**) T₃: Y=31.25X-92.44 (r=0.998**) T₄: Y=25.15X-58.55 (r=0.998**) T_5 : Y=27.84X-67.29 (r=0.998**) T_6 : Y=31.29X-142.93 (r=0.999**) where X was age in month ; Y was body weight ; and r was correlation coefficient. 3. The tendency for daily DM intake was that the bulls of higher TDN group consumed more DM. The daily DM intake(Y) was significantly(P$lt;0.01) correlated with age in month (X). T₁ : Y=0.304X+1.047 (r=0.953**) T₂ : Y=0.313X+2.215 (r=0.961**) T₃ : Y=0.305X+3.078 (r=0.934**) T₄ : Y=0.315X+0.948 (r=0.955**) T_5 : Y=0.316X+2.006 (r=0.961**) T_6 : Y=0.395X+1.480 (r=0.956**) 4. The linear and curvilinear relationship was found between body weight and DM intake with highly significant(r$gt;0.990 ; P$lt;0.01) correlation coefficients. 5. The digestibility of crude protein for 3 fattening periods tended to decrease as the level of TDN increased and that of NFE was much higher than that of other components studied. however, the digestibility of crude fiber tended to decrease as the ratio of concentrates in the ration increased for all 3 periods. 6. The daily TDN intake was increased as the level of TDN increased and the fattening stage progressed. The daily TDN intake(Y) was significantly(P$lt;0.01) correlated with age in month(X). T₁ : Y=0.245X+0.528 (r=0.952**) T₂ : Y=0.302X+0.801 (r=0.960**) T₃ : Y=0.379X+0.331 (r=0.947**) T₄ : Y=0.241X+0.625 (r=0.953**) T_5 : Y=0.341X+0.725 (r=0.957**) T_6 : Y=0.380X+0.248 (r=0.957**) 7. The linear and curvilinear regression equation to establish the relationship between body weight and TDN intake was derived with highly significant (r$gt;0.990 ; P$lt;0.01) for all treatments, The amount of TDN required per unit gain increased as the stage of fattening progressed. 8. The linear regression equation between DCP intake and body weight was derived with highly significant(r$gt;0.990 ; P$lt;0.01) correlation coefficients for all treatments. However, the mathematical relationship was not established between daily DCP intake and age in month since the correlation coefficients were insignificant. 9. The DM requirement was determined by the multiple regression equation, Y=0.0735X₁+3.3988X₂-1.5297 ; where X₁ was metabolic body weight (W^(0.75)_(kg)) and X₂, daily weight gain (㎏). The multiple co