The effects of γ-radiation on the properties and structures of isotactic polypropylene have been investigated in different medium and at different temperature.,The results showed that the intrinsic viscosity of polypropylene decreased with the increase of dose, and initial decrease in the intrinsic, viscosity is considerable. When the polypropylene irrradiated in air at room temperature, the degradation of polypropylene is predominate. The efficiency of cross-linking of polypropylene increased by irradiation in vacuum. When the temperature increased during irradiation, the gel point of polypropylene moved up to higher dose. Polypropylene irradiated in vacuum at 180℃ does not produce gel.,It was found by the X-analysis and infrared spectrum measurement that the degree of crystallinity and tacticity of polypropylene decreased remarkably with increasing temperature during irradiation.