The photoconductive properties of a uniform ultrathin multilayer film composed of alternating poly(p-phenylene vinylene) (PPV) and reduced graphene oxide (RGO) layers, fabricated on a poly(ethylene terephthalate) (PET) sheet are reported. The assembly of the two electron-rich layer components on the temperature-sensitive substrate is realized using a layer-by-layer-deposition technique under mild conditions and HI/H2O vapor treatment at 100 °C. This protocol is established to simultaneously convert the layer components to their conjugated counterparts, PPV and RGO in the multilayer films, whose total thicknesses shrinks to 50% of their original values due to lattice contraction. Furthermore, the surface roughness decreases significantly, in contrast to the results obtained from general chemical treatments. The PET sheets coated with (PPV/RGO)15 films exhibit a photocurrent of 115 μA at an illumination intensity of 1.1 mW and a photoresponsivity of 111.1 mA W−1 at an illumination intensity of 0.5 mW; these are among the best values yet achieved in carbon-based materials. The establishment of a method for fabricating (PPV/RGO) films on a temperature-sensitive transparent flexible sheet is crucial for the development of organic-based portable electronic devices.