Many experiments have been performed to investigate the thermal performance and thermal efficiency of a thermosyphon heat pipe charged with Al2O3-water/ethyleneglycol, (water-EG) and Al2O3-water/diethyleneglycol, (water-DEG) nanofluids. The heat pipe is fabricated from the high quality straight copper tube (with the outer diameter of 12 mm and length of 220 mm). The alumina spherical nanoparticles with mean size of 42-48 nm were well-dispersed, prepared and stabilized in water-EG and water-DEG base fluids at different particle concentrations using an ultrasonic homogenizer, magnetic stirrer as well as pH control in a constant temperature thermal bath. Influence of different operating parameters such as applied heat flux to the evaporator section, %charged value of working fluid, tilt angle of the heat pipe and volumetric concentration of nanoparticle on the thermal performance and efficiency of the heat pipe was experimentally investigated and briefly discussed. Results demonstrated that heat transfer coefficient of the heat pipe significantly increases, when nanofluids are used as possible working fluid and have a significant positive influence on the enhancement of thermal efficiency of the heat pipe. (C) 2014 Elsevier B.V. All rights reserved.