Temperature- and pH-responsive interpenetrating polymer network (IPN) hydrogels constructed with poly(vinyl alcohol) (PVA) and poly(diallyldimethylammonium chloride) (PDADMAC) using the sequential IPN method were studied. The characterizations of IPN hydrogels were investigated using Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). IPN hydrogels exhibited a relatively high swelling ratio, 180-360% at room temperature. The swelling ratio for the hydrogels depended on pH and temperature. DSC was used to determine the amount of free water in IPN hydrogels. The amount of free water increased with increasing PDADMAC content in the IPN hydrogel.