The concentration polarization effect of a macroligand on the affinity ultrafiltration of an important; glycopeptide antibiotic, vancomycin, was studied. The affinity ultrafiltration was carried out in a stirred cell, and the system was operated in a circulating and once-through mode. The macroligand was prepared by coupling the ligand D-alanyl-D-alanine to a water soluble polymer, dextran. The concentration polarization of dextran itself did not show any effect on vancomycin retention in the ultrafiltration cell. On the other hand, the retention of vancomycin was enhanced in the presence of concentration polarization of the macroligand on the membrane surface. The enhancement was due to the affinity binding of vancomycin to the macroligand in the concentration polarization layer. The observed affinity binding behaviors of vancomycin in the affinity ultrafiltration systems were in good agreement with that predicted by the thin film model coupled with the Langmuir isotherm and fast binding kinetics.