Thermoreversible copolymer hydrogel based on poly(ethylene oxide) and poly(hi-isopropyl acrylamide) has been prepared by gamma-radiation technique. The utility of C-13 n.m.r. spectroscopy in elucidating the structure and copolymer composition has been demonstrated. The volume transition as a function of temperature in these copolymers has been studied by swelling ratio measurements. Unlike poly(ethylene oxide) homopolymer gel, the copolymer gels show first order volume transition in the temperature range of 35-40 degrees C. These gels are easy to synthesise in any shape and size and are found to be having good mechanical strength even in the fully swollen state. They can have potential applications in controlled drug delivery, bioseparations and biomedical fields.