The thermal degradation of metal complexes formed by chitosan with Cu(II), Ni(II), Co(II), and Hg(II), at different metal concentrations, was studied by thermogravimetric analysis in a nitrogen atmosphere over the temperature range 25-800 degrees C. The results indicate that thermal degradation of chitosan and chitosan-metal ion complexes could be of one or two-stage reaction. In the thermal degradation of chitosan with metal complexes, the temperature of initial weight loss and the temperature of maximum weight loss rate decrease. Fourier transform infrared spectroscopy was used to probe the interaction of chitosan with metal ions. The bands of -N-H, -C=O, -C-O-C- groups of chitosan are shifted or change their intensity in the presence of metal. These changes in the characteristic bands are taken as evidence of the influence of metal ions on the thermal stability of chitosan. Broido's method was employed to evaluate the activation energies as a function of the degree of degradation. The presence of metal ions provoked a decrease in the thermal stability of chitosan, which became more marked when the concentration of metal was increased. The dynamic study showed that the apparent activation energy values of the main stage of the thermal degradation of chitosan-metal complexes decrease as the strength of the polymer-metal interaction increases. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114:2043-2052, 2009