Four types chitosan-based hydrogels have been prepared : cross-linked chitosan (cr-CS), cross-linked chitosan interpenetrating polyether polymer network (cr-CS/PE semi-IPN), cocross-linked chitosan and gelatin hybrid polymer network (CS/Gel HPN), and Chitosan/Pectin (CS/Ptn) ionic complex hydrogels. Water was used as a probe to elucidate heterogeneous structures of these hydrogels using differential scanning calorimetry (DSC) to study the physical state of water in the hydrogels swollen in distilled water. Results show that three states of water exist in all these hydrogels, while there are variations in the amount of nonfreezing bound water for different hydrogels. The correlation between water state and swelling kinetics data is discussed.