The aim of this work is to assess the possibility and usefulness of accessing low-temperature energy using a carbon dioxide-filled two-phase thermosyphon. Various parameters such as working fluid filling ratio, coolant mass flow rate, temperature difference between evaporator and condenser affect the heat transfer of thermosyphon system. In order to investigate the performance of thermosyphon system, we monitored the temperature distribution along the thermosyphon and measured input heat to evaporator section and output heat from condenser, as well. The results show that the heat transfer rate of thermosyphon increases with increasing mass flow rate and bath temperature. The results also show that the overall heat transfer coefficient increases with increasing coolant mass flow rate but decreases with increasing bath temperature. The reason of this decreasing is partly due to the enthalpy of vaporization of the carbon-dioxide decreases with increasing temperature.