The thermal degradation properties of chitosan and lactic and/or glycolic acid grafted chitosan have been studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TG) in the range of 25-500 degrees C. Both DSC and dynamic TG results show that the samples are thermal degraded easily after grafting the lactic and/or glycolic acid. From the isothermal TG experiments, the initial activation energy and the activation energy at different stages is obtained. The initial activation energy of all grafted samples is much lower than that of chitosan, especially for the sample GA/CS = 2 and it varies with degree of conversion. The FT-IR spectra of thermally degraded residues give an indication of the chitosan polyscaccharide ring degradation after 30 min in 280 degrees C, while sample GA/CS = 2 will degrade only after 15 min. (C) 2000 Elsevier Science Ltd. All rights reserved.