Soybean meal (SBM) is commonly used as protein supplement in the ration of high producing dairy cattle. It has a good palatability and acceptable amino acid balance. However, SBM has relatively low protein efficiency because of the extensive ruminal degradation. Recently, tannins have become a matter of interest in ruminant nutrition because of their potentially beneficial effects on decreasing the ruminal degradation of dietary protein (Barry and McNab, 1999). Several methods (in vivo, in vitro, in situ and solubility methods) have been proposed to characterize the dietary protein. Cornell Net Carbohydrate and Protein System (CNCPS) have a submodel in which crude protein is partitioned into five fractions with different degradation rates. Hence, the objective of this study was to determine the protein fractions of soybean meal treated with tannin in grape pomace.