In textile industry, advanced oxidation processes are used for degrading and removing color from dye baths which allow wastewater reuse. In this study, photochemical oxidation processes (UV-A/K₂S₂O₈, UV-C/K₂S₂O₈) and chemical oxidation process (dark/K₂S₂O₈), were investigated in a laboratory scale photoreactor for decolorization of the Reactive blue 19 (RB19) dye from synthetic textile wastewater. The effects of operating parameters such as potassium persulphate dosage, pH, reaction time and UV source, on decolorization have been evaluated. The results of direct chemical oxidation showed that 50% of the dye was been removed using K₂S₂O₈ in dark condition after 5h reaction time and photochemical oxidation showed that UV-C irradiation is more effective than UV-A for RB19 dye removal. The RB19 solution was completely decolorized under optimal potassium persulphate dosage of 5mmol/L and low-pressure mercury UV-C lamps (15w) in less than 30min. UV/K₂S₂O₈ experiments showed higher color removal performance under acidic conditions (pH=3), and in this condition with 5mmol/L of potassium persulphate, 78.5% COD has been removed after 3h irradiation time. The decolorization rate fitted to pseudo-first order kinetics with respect of dye concentration. The reaction rate constants for photochemical degradation of RB19 were 0.014 and 0.237 for UV-A/K₂S₂O₈ and UV-C/K₂S₂O₈ processes respectively.