Abstract Theanine (γ-glutamylethylamide) is the major “umami” (good taste) component of tea and its favorable physiological effects on mammals have been reported. An enzymatic method for the synthesis of theanine involving bacterial γ-glutamyltranspeptidase (GGT) was developed. The optimum reaction conditions were 200 mM Gln, 1.5 M ethylamine, and 0.4 units/ml GGT, pH 10. After 2-h incubation at 37 °C, 120 mM theanine was obtained, the conversion rate against Gln being 60%. Theanine was purified on Dowex 50 W×8 and Dowex 1×8 columns, and then identified by 1 H -NMR. This is the first report that a GGT, regardless of its source, can utilize an alkyl amine as an acceptor of the γ-glutamyl moiety in its transpeptidation reaction.