A recycle ultrafiltration membrane reactor was used for continuous production of antithrombotic peptides from enzymatic digestion of caseinomacropeptide (CMP). The kinetic parameters of the continuous process were determined on hydrolysis of various substrate concentrations and compared to those of the batch reactor. On the basis of peptide liberation, enzymatic activity was 10-fold lower during the continuous process (according to k c a t values) while the K m value was not modified. Taking into account these data, an experiment for bioactive peptide production from continuous hydrolysis of 34 g of CMP was carried out. After 6 h of continuous operation, permeate was concentrated by nanofiltration (volume concentration ratio = 12.5), freeze-dried, and the productivity as well as peptide yield determined. Although desired peptides were partially rejected by the ultrafiltration membrane during the continuous process, 2.65 g of these small molecules (500 to 780 Da) were obtained in the final powder.