This trial was carried out to investigate. the optimum feeding level of optimum concentrate level, when Korean native bulls were fed maize silage and water ad libitum. The level of concentrates in this trial were 1.0% (T₁), 1.5%(T₂) and 2.0%(T₃) of body weight, respectively. A total of nine Korean native bulls of average weight of 350㎏ with 3 heads per each treatment were fed for 90 days. The experimental design was a completely randomized design. The results obtained were summarized as follows: 1. Body weight gain of T₃ (122.6㎏) was significantly higher(P$lt;.05) than other treatments. 2. Daily intake of concentrate in T₃(7.8㎏) was significantly increased(P$lt;.05) and daily intake of maize silage was also significantly increased(P$lt;:.01) in T₁(27.5㎏). Feed conversion of DCP was higher in T₁(0.05㎏) and lower in T₂(0.79㎏). However, the differences were not statistically different(P$lt;.05). Feed conversion of TDN was higher in T₃(6.96㎏) without significant difference. 3. Rumen acetate concentration was the highest (P$lt;.05) in T₁(67.50%) and the lowest in T₃(62.35%). Rumen propionate concentration in T₁, T₂ and T₃ were 16.18%, 18.96% and 23.04%, respectively. 4. Dressing percent in T₃(58.90%) was significantly increased(P$lt;.05) and lean meat percent in T₁(47.4%) was significantly increased(P$lt;.05).