The interfacial sheer strength of an ultrahigh molecular weight (UHMW) polyethylene (PE) fiber/epoxy-resin system was greatly improved by the corona-discharge treatment of the fiber. The UHMW PE-fiber/epoxy-resin composite was prepared with corona-discharge-treated UHMW PE fiber. The mechanical properties of the composite sheet were determined by tensile testing. The tensile strength of the composite was also very much improved. However, the tensile strength of the composite was about one-half of the theoretical strength. This result was due to the molecular degradation of the PE-fiber surface caused by surface modification.