The surface of polytetrafluoroethylene (PTFE) and polyethylene terephthalate films was coated with plasma-polymerized hexamethyldisiloxane (PPHMDS) film in a triode glow discharge system. The dielectric properties of PPHMDS films and their durability, the partial discharge characteristics and the surface morphology of coated polymer films were investigated The lifetime of the coated PTFE films was longer than that of the uncoated PTFE films and varied with the preparation conditions of PPHMDS films. The maximum electrical pulse of the coated polymer film in a partial discharge electrode system was smaller than that of the uncoated polymer film. From observation of the deteriorated surface scars, it was shown that the PPHMDS film is effective for improving the partial discharge resistance.