A membrane-based chiral separation system for the separation of racemic tryptophan solutions is developed by the covalently binding betacyclodextrin onto the surface of commercial cellulose membranes. The immobilization process is monitored by XPS. AFM demonstrates the evolutionary transition of membrane surface morphology before and after the CD immobilization. Due to their different complexation with immobilized CD, dialysis transport experiments show D-tryptophan preferential permeability through the immobilized CD membranes, and the enantioselectivity is 1.10. A model based on the existence of a thin chiral solution layer of amino acid at the interface between the feed solution and the membrane has been proposed. This chiral separation model has been verified using the chiral separation results of racemic amino acids and binding constants of amino acids with CD. The effect of membrane's pore size on enantioselectivity has also been investigated. The immobilized CD membrane, having MWCO 1000, exhibits the highest enantioselectivity to the racemic tryptophan solution. (c) 2006 Elsevier B.V. All rights reserved.