The photodecolorization of the azo dye Direct Orange 34 (DO34) was investigated in TiO2 aqueous suspensions with artificial irradiation at 30°C. The experimental conditions were optimized by a 2(5) factorial design, using the decolorization percentage after 240 min irradiation as the response. The five factors considered were DO34 and TiO2 concentrations, stirring speed, air saturation, and adsorption time. The addition of hydrogen peroxide and sodium periodate as oxidants increased the decolorization rate.