Modification of chitosan (CTN), a natural biomaterial, leading to improved physical and chemical properties makes the polymer overcome the limitations on its application in biomedical fields. We have modified CTN using polyvinylpyrrolidone (PVP) in three ways, i.e., by blending (CTN: PVP), by graft copolymerization [poly(CTN-g-PVP)], and by free radical induced crosslinking [poly(CTN-cl-PVP)], varying the CTN to PVP ratio. The properties of all the modified and unmodified CTN studied included structural, thermal, mechanical, and water uptake capacity. Modification by blending imparted enhanced strength, toughness, glass transition temperatures, and thermal stability to the dry membranes. The equilibrium water content (EWC) of the membrane gels was investigated as a function of pH and ionic strength. Swelling ratio of the chemically modified membranes were found to be less sensitive to pH, with higher % EWC maintaining the gel integrity in both acidic and neutral media unlike the plain CTN. The hydrogen bonding and free volume of the films were found to play a major role in determining the properties of the type of modification. CTN membranes with enhanced water uptake capacities clubbed with optimum mechanical properties shall be a suitable choice for biomedical and controlled release applications. (c) 2006 Wiley Periodicals, Inc.