Ultrafiltration experiments for the chiral separation of racemic phenylalanine were performed with DNA-immobilized chitosan membranes having various pore sizes. Atomic analysis on the membranes showed that the chitosan membranes covalently bound six times more DNA than the cellulose membranes used in our previous study [A. Higuchi, Y. Higuchi, K. Furuta, B.O. Yoon, M. Hara, S. Maniwa, M. Saitoh, K. Sanui, Chiral separation of phenylalanine by ultratiltration through immobilized DNA membranes, J. Membr. Sci. 221 (2003) 207-218]. D-Phenylalanine preferentially permeated through DNA-immobilized chitosan membranes with a pore size < 6.4 nm [molecular weight cut-off (MWCO) < 67,000]. The binding affinity of a specific enantiomer due to the pore size of the DNA-immobilized membranes regulated the preferential permeation of the enantiomer through the membranes. L-Phenylalanine was adsorbed on the DNA-immobilized chitosan membranes with a pore size < 6.4 mn (MWCO < 67,000), while there was little difference between the adsorption Of D-phenylalanine and L-phenylalanine on the membranes with a pore size > 6.4 nm (MWCO > 67,000). The DNA-immobilized chitosan membranes were categorized as channel type membranes. (c) 2006 Elsevier B.V. All rights reserved.