pH-sensitive hydrogels were studied as a drug carrier for the protection of insulin from the acidic environment of the stomach before releasing it in the small intestine. In this study, hydrogels based on polyvinylpyrrolidone (PVP) networks grafted with acrylic acid (AAc) was prepared via a two-step process. PVP hydrogels were prepared by γ-ray irradiation (radiation dose: 25kGy, does rate: 5.36kGy/h), and then grafting by AAc monomers onto the PVP hydrogels with subsequent irradiation (radiation dose: 10kGy, dose rate: 3.0 kGy/h). These grafted hydrogels showed a pH-sensitive swelling behavior in various pH.