Photocatalytic activity of surface fluorinated TiO2-P25 (F-TiO2-P25) in the degradation of a chlorotriazine azo dye Reactive Orange 4 (RO 4) under ambient conditions was investigated in this study. Characterization of F-TiO2-P25 reveals that the catalyst has a strong absorption in the UV range and the presence of F atom in the catalyst. The degradation rate of RO 4 with surface fluorinated TiO2-P25 is three times faster than bare TiO2-P25. The quantum yield of UV/TiO2-P25 process is largely decreased by the increase of initial dye concentration, whereas in UV/F-TiO2-P25 process, the influence of initial dye concentration is less. Surface fluorination of TiO2-P25 enhanced the adsorption of RO 4 dye, while improving overall degradation rate. The optimum operating conditions of UV/ F-TiO2-P25 process for efficient degradation are reported. (C) 2009 Published by Elsevier B.V.