Polypyrrole (PPy) was deposited electrochemically on a platinum plate from a nitric acid solution of pyrrole. The PVC/PPy composite film was finally obtained by casting poly (vinyl chloride) (PVC) onto the PPy electrode from a tetrahydrofuran solution of PVC. The prepared composite film was irradiated at 90-degrees-C with a low-pressure mercury lamp in the stream of hydrogen gas saturated with steam, and the PVC film was dehydrochlorinated, leading to the formation of conjugated polyene. The electrical conductivity (sigma) of the PVC film in the irradiated composite film was revealed : sigma = 2.51 X 10(-5) S cm-1. By iodine doping, sigma was further enhanced up to 5.04 X 10(-3) S cm-1. The tensile strength of the irradiated composite film became larger than that of the original PVC film; i.e., the stress at break was : 461 (composite film); 401 kg cm-2 (PVC). These results were brought about by the doping of radical species to the conjugated polyene. The anion, NO3-, doped during the electrodeposition of PPy was photodecomposed to generate radical NO2. and this species was doped to the polyene, resulting in the formation of electrically conductive PVC and mechanically improved composite film.