A semi interpenetrating polymer network (IPN) of carboxymethyl cellulose (CMC) and crosslinked polyacrylic acid (PAA) has been prepared and its water-sorption capacity has been evaluated as a function of chemical architecture of the IPN, pH, and temperature of the swelling medium. The water uptake potential of the IPNs has also been investigated in inorganic salt containing aqueous solutions and simulated biological fluids. The IPN was characterized by IR spectral analysis, and the network parameters such as average molecular weight between crosslinks (M-c), crosslink density (q), and number of elastically effective chains (V-e) have been evaluated by water-sorption measurements. (C) 2004 Wiley Periodicals, Inc.