A corrugated fin for a composite heat exchanger for motor vehicles includes a condenser portion and a radiator portion. The radiator portion is larger in fin width than the condenser portion. The condenser portion and the radiator portion respectively have first and second louvers formed corresponding to the fin widths. The first and second louvers respectively have first and second louver slats inclined in a direction which is different for each of the condenser portion and the radiator portion so as to oppose each other, and an inclination angle of the second louver slats is smaller than an inclination angle of the first louver slats.