In order to utilize low enthalpy geothermal heat sources, a thermosyphon is a good device which can extract heat without using electric power. The heat transfer in the thermosyphon occurs through the circulation of a working fluid through a sequence of evaporation, vapor transfer, condensation, and liquid return. A two-phase thermosyphon system using carbon dioxide (CO2) as a working fluid has been investigated both experimentally as well as theoretically. Carbon dioxide is the only non-flammable and non-toxic fluid that has the potential to offer environmental safety in a system. A copper tube thermosyphon of total length of 1,000 mm with inside and outside diameters of 9.9 mm and 12.7 mm was developed by consisting of evaporator and condenser sections. The temperature distribution along the thermosyphon was monitored and theninput heat to evaporator section and output heat from condenser were measured as well. The effects of temperature difference between evaporator and condenser section and coolant mass flow rates on the performance of the thermosyphon were determined. The results indicate that the heat flux transferred increased with increasing coolant mass flow rate and temperature difference between evaporation and condenser section. The experimental analysis of the thermosyphon system confirms that the proposed system must be a reliable and highly efficient as well as environmentally friendly alternative to common ground-coupled systems.