This study was conducted to investigate the effects on in situ ruminal degradation of feed protein sources(soybean meal, P-SBM; dried distillers grain with solubles, P-DDGS; wheat bran, P-WB) treated with protease ascompared with conventional feed protein sources (soybean meal, SBM; dried distillers grain with solubles,DDGS; wheat bran, WB). There was no significant change in the chemical composition and amino acid profilesof enzyme treatment protein sources compared with the non-treated groups (p<0.05). But for treatment groups,the solid content and total amino acids were reduced by increasing the moisture content due to proteolyticconditions. On the entire incubation time in situ ruminal degradation rate of dry matter appeared higher intreatment groups compared to control groups (p<0.05), and that of the treatment groups suspended during 48hours were in the order of P-SBM (97.70%), P-WB (74.26%) and P-DDGS (72.39%). In particular, DMdegradation rate of enzyme treated DDGS significantly increased to 43.62%, 45.99%, 55.97%, 69.87% and 72.39%,respectively, incubated during 3, 6, 12, 24 and 48 hours in rumen (p<0.05). Also protein degradation rate ofP-WB and P-SBM significantly decreased compared to their respective non-treated sources; however, by contrast,in DDGS it was increased. For P-SBM, protein degradation rate significantly decreased at 6 and 12 hours, andfor P-DDGS it was increased at 3 and 6 hours of suspension times in rumen (p<0.05). In particular, proteindegradation rate of enzyme treated group suspended for 48 hours were in the order of P-SBM (91.81%), P-WB(86.36%) and P-DDGS (58.87%). This result suggests that protease treatment of feed protein sources might beutilized to increase the bypass ratio into post-rumen for wheat bran, soybean meal, and to improve theutilization of feed protein.