Decolorization of reactive brilliant red X-3B was studied by using an Fe-Ce oxide hydrate as the heterogeneous catalyst in the presence of H2O2 and UV. The decolorization rate was in the order of UV-Fe-Ce-H2O2 > UV-Fe3+-H2O2 > UV-H2O2 > UV-Fe-Ce >= Fe-Ce-H2O2 > Fe-Ce. Under the conditions of 34 mg l(-1) H2O2, 0.500 g l(-1) Fe-Ce, 36 W UV and pH 3.0, 100 mg l(-1) X-3B could be decolorized at efficiency of more than 99% within 30 min. The maximum dissolved Fe during the reaction was l mg l(-1). From the fact that the decolorization rate of the UV-Fe-Ce-H2O2 system was significantly higher than that of the UV-Fe3+-H2O2, system at Fe3+ = l mg l(-1), it is clear that the Fe-Ce functioned mainly as an efficient heterogeneous catalyst. UV-vis, its second derivative spectra, and ion chromatography (IQ were employed to investigate the degradation pathway. Fast degradation after adsorption of X-3B is the dominant mechanism in the heterogeneous catalytic oxidation system. The first degradation step is the breaking down of azo and C-N bonds, resulting in the formation of the aniline- and phenol-like compounds. Then, the breaking down of the triazine structure occurred together with the transformation of naphthalene rings to multi-substituted benzene, and the cutting off of sulphonic groups from the naphthalene rings. The last step includes further decomposition of the aniline structure and partial mineralization C of X-3B. (C) 2007 Elsevier B.V. All rights reserved.