Chitosan microspheres loaded Cu(II) were prepared using a precipitation method and heterogeneously crosslinked with glutaraldehyde. The abilities of the binary [Cu(II)/Glut-chitosan] system for binding two acid dyes, that is, Acid blue 25 (AB25) and Calmagite (Calma) were investigated. Sorption experiments were performed using a batch process at 25 degrees C and indicate pH dependence. Evidence for the modification of the raw chitosan polymer was provided by Fourier transform infra red spectral study, thermogravimetry, differential thermogravimetry, differential scanning calorimetry, and scanning electron microscopy analysis. Data gleaned from the thermal analyses, showed that the modification of the polymer decreases the thermal stability of the prepared materials with respect to that of the native one. The effecting factors during dye adsorption have been also studied. Thermodynamic and kinetic experiments were undertaken to assess the capacity and the rate of dyes removal on the surface of [Cu(II)/Glut-chitosan]. Experimental data were mathematically described using various kinetic models. The pseudo second-order equation was shown to fit the adsorption kinetics. The interpretation of the equilibrium sorption data complies well with the Freundlich adsorption model. Thermodynamic results indicate that the adsorption follows an exothermic process. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 3412-3424, 2012