The study was performed to evaluate the effects of soybean meal (T1) and corn distillers dried grains with solubles (DDGS, T2) hydrolyzed by microbial proteolytic enzyme of Protame® on milk production and protein contents in dairy cows. Total of nine Holstein cows (i.e., 1.67 ± 0.47 average parity and 23.7 ± 1.2 kg/d average milk yield) were randomly assigned to control, T1, and T2 (e.g., 3 animals per group) and treated for 4 weeks. Milk yield of 3 different groups was similar in the beginning of the study, however the milk yield of T1 and T2 treatment group had increased by 0.93 kg/d and 1.89 kg/d, respectively. Milk protein level of T2 treatment group was increased by 0.19% (e.g., 0.14 kg/d protein content), whereas there was no significant different in control and T1 group. In conclusion, blood metabolites were ranged in normal level, but BUN content was reduced from 19.03 mg/dl to 17.70 mg/dl in T2 treatment group. This result suggests that DDGS hydrolysate supplement efficiently increase milk yield and milk protein level as well as feed protein availability in dairy cattle.