In order to electrochemically modulate the optical property of transparent films, we have fabricated composite films consisting of gold nanorods having strong absorption bands in near infrared region and polythiophene exhibiting electrochemical activity. On applying electrochemical potentials of 800 and 0mV repeatedly, the plasmon band showed irreversible but consecutive changes due to the proceeding of aggregation of the nanorods in the film, while the absorption of polythiophene around 540nm changed reversibly. It was found the composite film could electrochemically modulate the color of the film, by utilizing the aggregation of gold nanorods in the electrochemically reversible polythiophene film.