Among the organic dyes these requirements are met most fully by polymethine dyes . However, their photoelectric characteristics have been little studied. In the present work such characteristics of novel thin film-type photoconductive polymeric composites (PPCs) based on an photoconductive naphthalimide-containing copolymer and symmetrical cationic polymethine dyes (CPDs), depending on their key structural factor (the length of the polymethine chain), were investigated for the first time.