The reusability of human serum albumin (HSA) as a stereoselective ligand for D,L-tryptophan separation in the affinity ultrafiltration (UF) system has been demonstrated by readjusting the medium pH from an acidic condition to a basic condition in this work The native and recovered HSA molecules exhibit a similar D,L-tryptophan separation factor of 5-7 under the same experimental conditions In addition, a high recovery percentage of HSA of above 80% has also been obtained by controlling both the membrane pore size and the membrane hydrophilicity. The combination of these two features (i.e. HSA reusability and high recovery) is very helpful for the large-scale industrial application of the affinity UF system in chiral separation. On the other hand, it has been found that the HSA binding capability to L-tryptophan could be affected by the solution ionic strength. A higher solution ionic strength may result in a decrease in amounts of L-tryptophan bound to HSA due to the changes in solution environment and HSA structure (C) 2010 Elsevier B V. All rights reserved.