The effect of copper adsorption on the mechanical properties of chitosan beads was investigated by measurement of creep modulus with a dynamic mechanical analyzer. Creep modulus changed drastically at a critical copper adsorption amount of 0.4 mol/mol of glucosamine unit. Creep modulus increased with increasing amount of copper up to 0.4 mol/mol, but decreased steeply as the amount of copper increased beyond 0.4 mol/mol. The variation in creep modulus with copper adsorption is discussed in terms of two models that describe the binding mode of transition metal to chitosan; the bridge model and the pendant model. (C) 2003 Wiley Periodicals, Inc.