The kinetic modeling of copper biosorption by Arthrobacter sp. immobilized in a hydroxyethyl methacrylate-based matrix is reported in this work. The resin-biomass complex (RBC) has been used for copper biosorption in different conditions according to a factorial experiment. Factors investigated were cross-linker (trimethylolpropane trimethacrylate) concentration, biomass concentration in the solid, and particles＇ granulometry. A maximum copper specific uptake of about 7 mg of Cu/g of biomass (dry weight) has been observed, in the case of a RBC with the following characteristics : 2% (w/w) cross-linker concentration, 8% (w/w) biomass concentration, and 425-750 mu m granulometry. The shrinking core model has been used for the fitting of experimental data. A good fit has been found in the case of controlling intraparticle diffusion in all experimental trials. The copper diffusion coefficient in RBC has been estimated from the slope of the regression lines. Values obtained for the diffusion coefficients do not differ from one another with respect to the estimated standard error. An average apparent copper diffusion coefficient of about 3 x 10(-6) cm(2)/s has been found.