Polyelectrolyte complexes (PEC) composed of various weight ratios of chitosan and hyaluronic acid (HA) were prepared. The PECs were formed by a reaction of the oppositely charged polymers. The characterizations of the PEC films were investigated by using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The PECs were found to swell rapidly, reaching equilibrium within 30 min, and exhibited relatively high swelling ratios of 250-325% at room temperature. The swelling ratio increased when the pH of the buffer was below pH 6, as a result of the dissociation of the ionic bonds, and with increments of temperature. Therefore, the swelling ratios of the films were pH and temperature dependent. DSC was used to determine the amount of free water in the PEC films, which increased with increasing chitosan content. (C) 2004 Wiley Periodicals, Inc.