Morphology of the high-oriented polypropylene suture differs from the unoriented film prepared by hot press, described in the previous papers. Electron beam irradiated homopolypropylene (PP)suture, copolypropylene (CPP) suture and the unoriented film were more stable than those of γ-irradiated ones. Also, during post-irradiation storage, it was found that the degradation of the CPP which consist of 6% ethylene unit was smaller compared with PP. Broken surface in the tied part of electron beam and γ-irradiated PP sutures was due to the oxidative degradation. On the contrary, in the case of electron beam irradiated CPP, there was no broken surface of its suture observed and its strength over one month of storage remained the same. Thus, sterilization by electron beam irradiation is possible in the CPP suture.