This paper deals with the heat exchange performance prediction of a counter flow type double-tube condenser for natural binary refrigerant mixtures composed of Propane/n-Butane or Propane/i-Butane. The local characteristics of heat transfer, mass transfer and pressure drop are calculated using a prediction method developed by the authors. The total pressure drop and the overall heat transfer coefficient are also evaluated on various heat exchange conditions. The calculated results of the natural refrigerant mixtures are compared with those of pure refrigerant HCFC22. In conclusion, natural binary refrigerant mixtures composed of Propane/n-Butane or Propane/i-Butane are appropriate candidates to replace HCFC22 from the viewpoint of heat transfer characteristics.