Electrospinning is an useful technique to produce nanofiber webs. Since electrospun nanofiber webs have a nanoporous structure, they have a potential application for a polymer electrolyte or a separator. Poly(vinylidene fluoride) (PVDF) is used as one of polymer electrolyte binders. We studied application of eletrospun PVDF nanofiber webs as an electrolyte binder or a separator for a battery. Diameters of the electrospun PVDF nanofibers were 100–800nm. The electrospun PVDF nanofiber web was thermally treated at 150–160°C to improve the physical property and dimensional stability. The tensile strength and elongation at break as well as the tensile modulus were notably improved by the thermal treatment. Level of cryatallinity of the electrospun PVDF nanofiber was increased by the thermal treatment. The ion conductivity of the polymer electrolyte formed from the electrospun PVDF nanofiber web and 1M LiN(CF3SO2)2 electrolyte solution was 1.6–2.0 × 10−3 S/cm. The electrospun PVDF nanofiber mat was treated with ethylene plasma to use as a separator. The ethylene plasma-treated mat showed a role of shutter by melting the polyethylene (PE) layer grafted on the PVDF nanofibers.