The creep behavior and creep failure law of polypropylene (PP) were investigated by using a multifunctional stress-aging testing machine under different aging environmental conditions (temperature, UV, and stress). Photoinduced changes in samples were studied using gel permeation chromatography and X-ray photoelectron spectrometer. Surface morphologies were also observed by scanning electron microscopy. It was found that there is a critical failure strain (epsilon(crit)) for PP during the creep course. Once the creep deformation exceeds the epsilon(crit) creep failure of PP takes place very rapidly. The value Of epsilon(crit) is independent of the tensile stress and UV irradiation, whereas it is only affected by the temperature and the nature of the PP, such as molecular weight and molecular structure. With increasing temperature, the value Of epsilon(crit) increases gradually. In addition, the creep rate of PP increases rapidly with increasing tensile stress and temperature as well as under irradiation with UV light. This study may provide a new way to predict the service lifetime of PR POLYM. ENG. SCI., 49:1375-1382, 2009. (C) 2009 Society of Plastics Engineers