A novel optical resolution method for D,L-phenylalanine in which an enzyme reaction and a membrane extraction are combined has been designed. In the first stage only the L-isomer of the racemic phenylalanine methyl ester was selectively hydrolyzed by the enzyme alpha-chymotrypsin. Further, the unreacted ester was selectively recovered from the mixture of the transferred amino acid and the ester form by a membrane extractor. Effects of operation conditions in the enzyme reaction and the membrane extraction on the separation efficiency were investigated. The pH in the material sources is found to be an important factor in the activity and selectivity for the enzymatic resolution. A novel immobilized enzyme enables the expensive enzyme to be reused in the feed solutions. The hollow-fiber membrane extractor was a good separator for an amino acid and its ester derivative, because only the ester was selectively extracted into an organic phase. The novel separation system becomes a very useful process for the optical resolution of amino acids by combining the enzyme reaction with a membrane extraction.