Pyruvic acid-producing Escherichia coli W1485lip2 was transformed with the plasmid of KT901EA that carries the tryptophanase structural gene from Enterobactera aerogenes SM-18 downstream of the tac promoter. In the course of culture of the transformant in a pyruvic acid fermentation medium, isopropyl-beta-D-thiogalactopyranoside and other nutrients were supplied to the medium to induce tryptophanase expression. After 32-h culture, 28.6 g/l of pyruvic acid had been produced, and a large amount of tryptophanase had been accumulated in the cells. By addition of ammonia and indole to the culture broth, the enzymatic synthesis of L-tryptophan was then started. Our results showed that 23.7 g/l of L-tryptophan had been produced after reaction for 36 h (total 68 h).