A polyvinylpyrrolidone（PVP）/chitosan（CHI）blend hydrogel was prepared with ammonium cerous sulfate as initiator and glutaraldehyde as crosslinking agent.It was found that the glass-transition temperature（Tg）of the blend increased with increasing of PVP content.Microzone of CHI and PVP were observed over the surface of hydrogel from SEM micrographs.The swelling ratio of the hydrogels increased with increasing of PVP content，decreasing PVP molecular weight or increasing deacetylation degree of CHI.At normal temperature，there were three endothermic peaks observed from DSC thermograms of the hydrogel with a CHI∶PVP ratio of 1∶2 due to water loss，and the content of free water，freezing bond water and non-freezing bond water are 42.7%，43.3% and 14.0% respectively.However

there was only one peak when the CHI∶PVP ratio was 1∶8.A group of peaks were observed at 0℃，38℃ and 53℃ from DSC thermograms of the hydrogel is the freezing state of -123℃.It was resulted from the transition from crystalline water (formed from free water and freezing bond water at a low temperature) and back to free water and freezing bond water at a higher temperature.