Abstract Most of the thermodynamic system interactions involve energy (heat) in one form or the other i.e., heat is either added to or is removed from the system to ensure sustained operation. Heat pipes are novel devices that work on the principle of evaporation and condensation of a working fluid to help transfer heat from a source to a sink. The heat pipes which do not use wicks or capillary structures, but rely on gravity to transport condensate back to evaporator is called a thermosyphon heat pipe. The heat pipes generally use conventional fluids to remove the heat. In order to enhance the heat transfer rate of heat pipe, nanofluids are being used because of their enriched thermal properties as compared to conventional fluids. The paper throws light on an investigation done on a thermosyphon heat pipe to determine its thermal performance. The thermosyphon heat pipe was tested for various values of heat input from 40 W to 200 W with two working fluids – DI water and Aluminium nanofluid. A nano-particle concentration of 1% was used in the nanofluid. Experiments performed under varying angles of inclination of thermosyphon heat pipe suggests an increase in its performance by 41% when nanofluid was used as working fluid instead of DI water. Also, a peak efficiency of 88% was obtained at an inclination angle of 60°.