A process for efficient production Of L-phenylalanine catalyzed by a coupled enzymatic system of transaminase and aspartase with two organisms was developed. One strain, Escherichia coli EP8-10 produces significant transaminase and less aspartase under incubation in the glucose-beef extract medium. In the presence of 50 mg/ml cells of EP8-10, 0.24 mol/l phenylpyruvic acid (PPA) was converted to L-phenylalanine (L-Phe) in 8 h with L-aspartic acid as an amine donor, the conversion rate was 97%. Another strain, E. coli EA-1, a mutant strain of ATCC 11303, produces significant aspartase and less transaminase. L-Aspartate (L-Asp), the amine donor, could be produced by EA-1 from fumarate (Fu) and ammonia. In presence of the mixture of EP8-10 and EA-1 cell, L-phenylalanine was efficiently produced from PPA and ammonium fumarate. An optimum reaction condition of the coupled enzymatic system is as follows: the concentration ratio of two cells as 0.4:1 (EA-1 to EP8-10), concentration ratio of two substrates (PPA to Fu) as 1:1.2 (mol). When concentration of PPA was 0.24, 0.233 mol/l (38 g/l), L-phenylalanine acid was accumulated by the conversion rate up to 97%. L-Phenylalanine production is more economical by the coupled enzymatic system, since one of the substrates L-aspartate was replaced by the relative cheap fumaric acid. (C) 2003 Elsevier Inc. All rights reserved.