A chitosan (CS) derivative, N-(4-methylimidazole)-chitosan (MIC), was synthesized, and a cobalt (II) complex of bis(salicylideneethylene diamine), (CoSalen), was immobilized on it. The structure of the polymer-immobilized CoSalen was characterized by elemental analysis, IR, XPS, fluorescence and ESR spectroscopy. It was demonstrated that the immobilization of CoSalen was realized through the coordination of a nitrogen atom of the pendant group, imidazole in MIC, to the Co(II) in CoSalen. The immobilized polymer complex is more efficient than the corresponding monomeric complex in catalyzing the oxidation of DOPA using oxygen. The results may be attributed to a site isolation effect offered by the supporting polymer chain. A mechanism similar to that for enzymatic catalysis was proposed. (c) 2006 Wiley Periodicals, Inc.