Abstract: The oxidation using UV-Fenton reagent has been found to be a promising treatment method for the effective decolorization and degradation of dyes. The decolorization of the reactive blue dye KN-R was investigated using Fenton and UV/Fenton processes. The effects of solution pH, initial dye, H2O2, Fe2+ concentrations, respectively, were studied and optimal conditions determined. The optimized treatment conditions are the following: pH 3.0, 30 mg L 1 (Fe2+), 10.2 g L 1 (H2O2) for a reaction time of 30 min. The KN-R dye degradation was found to be dependent on the dye concentration such that the higher the dye concentration, the lower the decoloration and degradation efficiencies. The UV/Fenton process showed higher decoloration rate than the Fenton process and 98% was achieved in about 10 min of the reaction time. The effect of iron source and NaCl were studied. Finally, kinetics involved in KN-R degradation were also calculated and the rate constants were found to be proportional to hydrogen peroxide concentration as well as ferrous ions concentration.