The aims of this work are to investigate the ozone mass transfer in the hollow fiber membrane contactor for ozonation of dye solution and to study the effect of dyeing auxiliary reagents on decolorization performance. Effects of hydraulic retention time (HRT) in the system and membrane on color removal were also investigated in the continuous ozonation membrane contacting system. Dye used in this experiment was C.I. Reactive Red 120 (RR 120) and sodium carbonate (Na2CO3) and sodium chloride (NaCl) were used as additives. It was found that the ozone flux increased with increasing liquid velocity for water and dye solution as a liquid phase. Change in gas velocity did not influence the ozone flux. Therefore. the main mass transfer resistance for ozonation in membrane contactor was in liquid phase for both cases. The presence of Na2CO3 in the dye solution resulted in increasing the ozone flux, conversely, the ozone flux decreased when NaCl was added. Decolorization performance by ozone was inhibited when Na2CO3 existed in the dye solution. For ozonation membrane contacting system, the dye color removal performance increased with increasing HRT of the system. Additionally, decolorization of dye solution increased with decreasing HRT in the membrane module. (C) 2008 Elsevier B.V. All rights reserved.