Laccase-catalyzed L-DOPA oxidation in an oxygen-saturated water solution was studied in a y-shaped microreactor at different residence times. In a given microreactor geometry, up to 87% conversions of L-DOPA were achieved at residence times below 2 min. A two-dimensional mathematical model composed of convection, diffusion, and enzyme reaction terms was developed. Enzyme kinetics was described with the double substrate Michael is-Men ten equation, where kinetic parameters from previously performed batch experiments were used. Model simulations, obtained by a non-equidistant finite differences numerical solution of a complex equation system, were proved and verified in a set of experiments performed in a microreactor. Based on the developed model, further microreactor design and process optimization are feasible. (C) 2009 Elsevier B.V. All rights reserved.