This work reports the preparation of 2-hydroxyethyl methacrylate (HEMA)/N-vinyl-2-pyrrolidone (NVP) interpenetrating polymer network (IPN) hydrogels by UV-initiated polymerization in the presence of free radical photoinitiator Darocur 1173 and cationic photoinitiator 4,4'-dimethyl diphenyl iodonium hexafluorophosphate. The polymerization mechanism was investigated by the formation of gel network. The structure and morphology of the HEMA/NVP IPN hydrogels were characterized by fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that the IPN gels exhibited homogeneous morphology. The dehydration rates of HEMA/NVP IPN hydrogels were examined by the gravimetric method. The results revealed that the hydrogels had a significant improvement of antidehydration ability in comparison with poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel embedded physically with poly(N-vinyl-2-pyrrolidone)(PVP). (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1851-1858, 2010