The heat transport characteristics of a thermosyphon are experimentally investigated using R 113, methanol and water as the working fluid. The condensation heat transfer at the cooling section shows a trend similar to the Nusslelt's prediction for its temperature difference, while the measured values are considerably lower when the upward vapor velocity is high, as in the case of water. Based on the characteristics in heat transfer at the cooling and heating sections, non-dimensional expressions are derived for relating the heat transfer at the cooling and heating sections, non-dimensional expressions are derived for relating the heat transport rate of thermosyphons to the temperature difference between the heating and cooling sections.