The aim of this study was to investigate the effects induced by three different sterilization methods [steam, gamma-radiation, and ethylene oxide (EO)] with different dose or time period of sterilization by means of Fourier transform infrared spectroscopy, X-ray diffraction, and assessments of molecular weight and degree of deacetylation. The experiment results clearly showed that the steam sterilization greatly darkened the color of chitosan powder; gamma-irradiation strongly depolymerized the chitosan especially at irradiation dose above 10 kGy; and exposure to EO led to minor change in crystallinity and network structure of chitosan powder. Therefore, these three methods have their respective advantages and disadvantages, suggesting that the selection of the sterilization method of chitosan should depend upon the specific requirement of the final application. (c) 2007 Wiley Periodicals, Inc.