Abstract Evaluation of the degradability of irradiated polymers under natural environmental conditions may give useful information about the possible rapid degradation of waste polymer materials for environmental conservation. The degradability in various environments of poly(propylene-co-ethylene), CPP, after irradiation has been investigated. The degradability of the CPP in the natural environment, evaluated by strength and elongation tests, during storage after irradiation was slower than that of polypropylene (PP). Thus, CPP required a larger dose to achieve the same degradability as PP. However, molecular scission of the CPP during roof storage was almost the same as that of PP. The CPP has a lower crystallinity and a smaller spherulite size than PP. Thus, the degradability measured by the tension test of irradiated CPP during storage was different from that of PP. However, it was confirmed that irradiation was effective in accelerating degradation of CPP during outdoor storage.