The current studies were conducted to determine the effect of feeding value of brewers grain(BG) and beet pulp(BP) for lactating cows compared to corn silage and hay with rice straw. Twelve lactating cows were alloted into 3 × 3 Latin square method to determine the effect of feeding BG and BP with rice straw on lactating performance. Whole tract nutritive digestion, ruminal dry matter and protein degradation, and protein retention rate were also examined with sheep. The results obtained from present experiments are as follows; 1. Daily milk yield of cows fed corn silage-hay (CS-H), rice straw-beet pulp-brewers grain (RS-BP-BG) and rice straw-beet pulp (RS-BP) was 18.12, 19.21 and 18.32㎏, respectively. Cows fed RS-BP-BG had the highest milk yield(P$lt;0.05). Milk fat and liveweight were not affected by diets. 2. No significant differences on ruminal C₂ and C₄ concentrations were observed among experimental feeds, but C₃ concentration in CS-H, RS-BP-BG and RS-BP were 13.60, 37.18 and 31.82 mM/L(P$lt;0.05). Sheep fed CS-H had the highest ruminal P (6.2), while those fed RS-BP showed the lowest ruminal P (5.7) (P$lt; 0.05). 3. Percent dry matter disappearances of experimental diets containing CS-H, RS-BP-BG and RS-BP in the rumen were 66.7, 63.3 and 69.2%, and the protein disappearances from nylon bags incubated for 24 hrs were 66.7, 61.3 and 67.1%, respectively. 4. Whole tract dry matter, protein, NDF and ADF digestion was influenced by dietry treatment with highest digestibility in sheep fed RS-BP (P$lt;0.05), while no significant differences on digestibilities of ether extract and crude ash were observed among diets. 5. Sheep fed CS-H had the highest total N intake, and RS-BP had the highest N retention (35.86%) (P$lt; 0.05). 6. Total viable counts of bacteria in the rumen of sheep fed CS-H, RS-BP-BG and RS-BP were 3.63×10^9, 3.91×10^9 and 4.05×10^9/㎖, and cellulolytic bacteria in rumen content was 0.3×10^7, 1.5×10^7 and 1.1×10^7/㎖. 7. Gross income was highest for cows fed RS-BP-BG. In conclusion, the lactating performance was improved when cows were fed RS-BP-BG as a replacement of CS-H