This article presents the preparation of the hydrogel of poly(N-propionylethyleneimine) and its interpenetrating polymer network (IPN) hydrogel containing polyacrylamide by means of gamma-ray radiation and a study of the phase transition temperature of these hydrogels. As a result, the hydrogel of the crosslinked poly(N-propionylethyleneimine) exhibited swelling below and shrinking above the phase transition temperature (about 61 degrees C), as well as the lower critical solution temperature (LCST) of the liner polymer-water system. The experiment also showed that the LCST of the IPN hydrogel could be adjusted by the incorporation of the second component polyacrylamide.