The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO 2-P25. Response surface methodology, based on a 3 2 full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO 2 (0.1-0.9 g/L) and H 2O 2(1-100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO 2/L and 50 mmol H 2O 2/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min -1. Based on these results, this photocatalytic process has promise as an alternative for the treatment of textile effluents. © IWA Publishing 2012.