A base coat coating composition which is able to suppress cracking of a metal thin film, even when a tough top coat layer capable of satisfactorily protecting the metal thin film is formed on the metal thin film, and even when a heat resistance test is performed, as well as a composite film and a method for producing the composite film. Specifically, a base coat coating composition used for undercoating a metal thin film formed on a metal substrate, and containing a coating film-forming component which contains at least 30% by mass of an epoxy (meth)acrylate having a cyclic structure and has an average molecular weight between crosslinks of 180 to 1,000, as well as a composite film having a base coat layer obtained from the base coat coating composition, and a method for producing the composite film.