Crosslinking on chitosan was conducted with gamma-glycidoxypropyltrimethoxysilane (GPTMS) with in situ formation of chitosan-silica hybrid membranes. The formed silica structure was observed with Si-29 NMR, scanning, and transmission electronic microphotograghy. Energy dispersive X-ray Si-mapping analysis demonstrated the homogeneous dispersion of silica in chitosan polymer domains. The formed chitosan-silica hybrid materials exhibited improved thermal stability and low degree of swelling in water. The hydrophilicity of chitosan membranes was maintained after the crosslinking reaction. This approach provided a convenient way to prepare crosslinked chitosan and chitosan-silica hybrid materials and the materials were potentially applied in biomaterials and separation membranes. (C) 2004 Published by Elsevier Ltd.