High producing or rapidly growing ruminants require more high quality protein than is provided by rumen microorganisms. This protein can be supplied by increasing the amount of dietary protein escaping degradation in the rumen. Solvent-extracted soya bean meal (SBM), which is a commonly used protein supplement to high producing dairy cows, is palatable with a well-balanced amino acid composition. However, SBM proteins are extensively degraded in the rumen. Attempts to decrease the rate and extent of ruminal degradation of soya bean meal proteins involved treatment with physical and chemical agents. Recently Tuncer and Sacakli (2003) reported that xylose reduce soya bean meal crude protein (CP) degradation in the rumen. To our knowledge, little information is available concerning the type of proteins of un- and xylose treated soya bean meal that leaves the rumen undegraded. The main objectives of our research were to evaluate the degradation of un- and xylose treated soya bean meal proteins by using SDS-PAGE and determine Effective Rumen Degradation (ERD) and intestinal digestibility of un- and xylose treated soya bean meal CP.