We present a kinetic model for the synthesis of amoxicillin from p-hydroxy-phenylgcine methyl ester and 6-aminopenicillanic acid, catalyzed by penicillin G acylase immobilized on agarose, at 25 degrees C. Michaelis-Menten kinetic parameters (with and without inhibition) were obtained from initial velocity data (FH 7.5 and 6.5). Amoxicillin synthesis reactions were used to validate the kinetic model after checking mass transport effects. A reasonable representation of this system was achieved under some operational conditions, but the model failed under others. Nevertheless, it will be useful whenever a simplified model is required, e.g., in model-based control algorithms for the enzymatic reactor.