A series of physically crosslinked complex hydrogels of poly(vinyl alcohol) (PVA) and sodium carboxymethylcellulose (CMC) were prepared via physical mixing and a freeze/thaw technique. The morphology of the CMC/PVA complex gels was analyzed with differential scanning calorimetry and wide-angle X-ray diffraction. It was found that the crystallinity and melting temperature of the complex gels decreased, whereas the glass-transition temperature increased, with an increase in the content of CMC. The reswelling of the complex gels was pH-responsive and relied on the content of CMC and the freeze/ thaw cycles. A network structure model of the complex gel was presented. PVA crystalline regions served as physical crosslinks; the interaction between CMC and PVA resulted in intramolecular entanglements. It was also found that the model drug hemoglobin was released completely from the complex hydrogels in 4 h, and its release rate increased with an increase in the content of CMC. (c) 2007 Wiley Periodicals, Inc.