Bovine serum albumin was hydrolyzed with trypsin in a batch stirred tank reactor. The influence of operating parameters on the degree of hydrolysis was investigated by pH-stat method. Molecular weight distribution of hydrolysates was analyzed by high performance size-exclusive chromatography. The kinetic model of hydrolysis reaction was studied by a lumping technique. The hydrolysates were combined into several lumps according to their molecular weights. Reaction of the lumps was described with intrinsic kinetic equations, and the lumping kinetic model for bovine serum albumin tryptic hydrolysis reaction was established. The rate constant of each reaction was estimated by Marquardt method in two steps from lower level to upper level. The reliability of the model was tested by comparing the computed values with the experimental values. (c) 2004 Elsevier Ltd. All rights reserved.