pH-Sensitive amphiphilic hydrogels were synthesized by radiation copolymerization of ethylene glycol vinyl ether (EGVE), butyl vinyl ether (BVE) and acrylic acid (AA) in the presence of crosslinking agent, diethylene glycol divinyl ether (DEGDVE). The results of the swelling experiments indicated that the hydrogel which has 60:40:5 comonomer ratio (mol% of EGVE:BVE:AA in monomeric mixture) is pH-sensitive. While the hydrogel is in a fully hydrated form at pH > 6, it extensively dehydrates below pH 6. A two-stage volume phase transition was observed in the range of pH 6.0-7.0 and 7.5-8.0. In addition, the equilibrium water contents of the gels decreased with increasing temperature from 4 to 37°C by following the non-Fickian diffusion mechanism. The utility of pH-sensitive gels in delivery of protein based drugs was investigated. Bovine serum albumin (BSA) loaded gels were prepared and protein release was examined by fluorescence spectroscopy in the range of pH 2-9. While the protein release was very low at pH 2, readily high amount of BSA were released at pH > 6. It was concluded that the pH-sensitive EGVE-BVE-AA terpolymers may be suitable for the oral administration of protein based drugs as a carrier through gastrointestinal (GI) tract. © 2004 Elsevier B.V. All rights reserved.