Temperature sensitive fast response poly (N-isopropylacrylamide) (PNIPAAm) hydrogels have been synthesized by simultaneously polymerizing and crosslinking NIPAAm monomer in aqueous solutions by electron beam (EB) and gamma irradiation and their equilibrium and dynamic swelling behavior have been investigated. The weight change kinetic studies show that radiation crosslinked hydrogels swell/deswell to attain equilibrium at much faster rate with diffusion coefficient values D≈4.0×10 −7 cm 2s −1 and 15×10 −5 cm 2s −1 for swelling and deswelling respectively. The effect of radiation characteristics such as irradiation dose, dose rate on the lower critical solution temperature (LCST), gelation dose ( D g) and swelling behavior of the resultant PNIPAAm gels has also been investigated.