A mathematical model that incorporates both mass transfer effects and reaction kinetics was developed for an aqueous/organic two-phase reaction system. The hydroxylation of phenol by tyrosinase was examined as a model reaction. A mildly agitated reactor was employed to maintain a quiescent liquid-liquid interface and stable enzyme activity. Mass transfer rate was expressed as a function of bulk concentration of substrate in both phases, partition and mass transfer coefficients. The model fitted the experimental data well for various reaction conditions such as initial substrate concentration, phase volume ratio, agitation speed and organic media used. Simulations showed that the conversion of substrate was strongly dependent on the initial substrate and enzyme concentrations and phase volume ratio. A lower fraction of organic phase led to an improved product partition and a higher fraction of organic phase to a greater substrate partition. The proposed model could be used for the optimization of two-phase enzymatic reaction systems.