The invention relates to a resonant tag including an insulating thin film and coiled circuits made of a metal foil respectively formed on both sides of the insulating thin film. The coiled circuits are formed in an electrically connected relation to each other with a space at the center of the insulating thin film. Said both coils are almost superimposed on each other to form a capacitor, thereby constituting an LC circuit. The area of a portion of each side of the thin film, said portion being surrounded by the innermost peripheries of both coils and having no metal foil on both sides, is controlled to at least 16% based on the whole area of said one side of the tag, whereby a resonant tag having an area of at most 700 mm.sup.2 can be obtained.