Polyethylene glycol (PEG)-linked manganese halogenated porphyrins (Chart 1) catalyzed oxidation of azo dyes (Chart 2) by H2O2 under mild conditions such as pH 8.0 at 25 degrees C especially when imidazole was present, causing the decoloration of azo dyes. The decoloration of azo dyes by synthetic manganese porphyrins under mild conditions was first reported. The decoloration rate depended on the structures of the porphyrins, in which the largest rate was observed in the presence of PEG-MnDCPP. The decoloration may be contributed by radical species rather than electrophilic species, consistent with the side-chain oxidation of toluene. Kinetics on polyethylene glycol-linked manganese porphyrin-catalyzed decoloration of C.I. Acid Orange 7 by hydrogen peroxide revealed that the decoloration was contributed at the oxidation process by manganese porphyrins with hydrogen peroxide in the polymer domain rather than the complex-formation process between manganese porphyrins and azo dyes.