In this work we describe the application of a new non-soluble and non-porous complex with copper ion based on ethylene glycol diglycidyl ether (EGDE), methacrylic acid (MAA) and 2-methylimidazole (2MI) in the decolorization of an azo dye Methyl Orange (MO) as a model pollutant at room temperature. The complex with copper ion was studied by ESR and SEM and was tested as a heterogeneous catalyst for H2O2 activation. A possible mechanism of interaction involves the production of hydroxyl radicals (confirmed by ESR), dioxygen and water. The Cu(II)-polyampholyte/H2O2 system acted efficiently in the color removal of MO. The adsorption and oxidative degradation of the azo-based dye followed pseudo-first-order kinetic profiles, and the rate constant for degradation had a second-order dependence on copper ion content in the mixture. A removal of MO higher than 90% was achieved in 20 min at pH 7.0, combining 0.8 mM of complexed copper ions in the mixture with 24 mM hydrogen peroxide. The dye adsorbed on the polyampholyte following a L4-type isotherm with 4.9 μmol g-1 maximum loading capacity and 3.1 μM dissociation constant for the first monolayer. © 2008 Elsevier B.V. All rights reserved.