The swelling behavior of cylindrical poly(vinyl alcohol) (PVA) hydrogels, prepared by means of γ-ray irradiation technique with different irradiation doses have been investigated. The cylindrical gels with ca. 0.2 mm diameter were immersed in various concentrations of Congo red (CR) solutions, and the time course of the swelling degree of the gels were microscopically measured. The swelling degree was increased with the increase in polymer content and time course, but decreased with increasing the irradiation dose. The sorption experiment of CR onto PVA hydrogels was also carried out. CR concentrations of the solutions before and after the sorption were determined spectrophotometrically. Higher irradiation dose of hydrogels had higher dye uptakes. This result reveals that the gels were strongly crosslinked, and the CR anions were bound to PVA as bridges between the hydroxyl groups of PVA. The effect of incorporation of dye on the chemical structure of PVA hydrogels was studied by using differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The results of DSC analysis showed that the melting temperatures of CR-PVA hydrogels are significantly lower than that of PVA hydrogels alone. It is possible to conclude that PVA structure has a significant loss of crystallinity when PVA interacts with CR. FTIR spectra of PVA hydrogels and CR-PVA hydrogels showed the absorption regions of the specific functional groups associated with hydroxyl groups of PVA confirming the formation of cross-links between them. The results showed that the interaction between PVA hydrogels and CR affect the swelling and sorption properties of the hydrogels.