The decolorization of azo dye by titanium dioxide (TiO2) with 360nm ultraviolet (UV) light was studied in a batch reactor. Response surface methodology was applied to optimize four independent parameters, viz. UV light intensity, the concentration of TiO2, initial pH, and stirring speed, in the photocatalytic degradation process of the dye Reactive Red 239. To obtain the mutual interaction between these four parameters and to optimize these parameters during the process, a 2(4) full-factorial central composite design (CCD) and response surface methodology were employed. The results of our experiments indicate that the concentration of TiO2, exhibits a significant positive effect on the efficiency of decolorization, whereas initial pH shows a significant negative effect. The optimized condition of the photocatalyfic degradation of Reactive Red 239 is as follows: UV light intensity, 16.08 W/m(2); TiO2 concentration, 3.06 g/l; initial pH, 2.64; stirring speed, 880 rpm. Under this condition, the maximal decolorization efficiency of 99.82% was achieved. (c) 2005 Elsevier B.V All rights reserved.