Ozone mass transport in the flat-sheet membrane contactor with chemical reaction in the liquid phase has been investigated. The ozone mass transfer coefficients without reaction in the liquid phase were indirectly determined by the oxygen transfer measurement with the steady state method. The oxidation of nitrite to nitrate was utilized to study mass transfer with ozonation. The ozone fluxes and the enhancement factors (E) were predicted by the facilitation of the resistance-in-series model together with the film and surface renewal models. The performance of the designed membrane modules was assessed by the decolorization of NOM solutions and indigo reagent 1. The ozone mass transfer coefficients from oxygen transport experiments were considerably higher than those calculated from the available correlations but provided good predictions for ozone fluxes for pure water. The ozonation accelerated mass transfer in membrane contactor by 6-100 times in this study. The experimental results validated the proposed methods for the predictions of the ozone fluxes and the enhancement factors. The average discrepancies between the experimental and calculated results were 6% for the ozone flux predictions and 3%. for them enhancement factor predictions. The resistances to the ozone mass transfer with and without chemical reaction were controlled by the liquid film. The ozone consumption for the NOM decolouriration in the membrane contactor was considerably lower than that in a conventional bubble column. (C) 2004 Elsevier B.V. All rights reserved.