Polypropylene (PP) was irradiated by γ-rays, and then foamed with supercritical carbon dioxide. The effect of absorbed dose on melting temperature, shearing viscosity, and melt mass-flow rate (MFR) of radiation modified PP was characterized by means of differential scanning calorimeter (DSC), advanced rheology expand system (ARES), melt flow rate testing instrument, and the morphology of PP foam was investigated by scanning electron microscopy (SEM). The results showed that the melting temperature and viscosity of PP decreased after γ-ray irradiation. The foamability of radiation modified PP is improved and a higher foam volume expansion ratio is obtained after radiation modification. At a given foaming pressure, foaming of radiation modified PP needs a lower temperature than that of original PP.Cited