The influences of bentonite-containing nanofluid utilization as the working fluid in a heat pipe consisting of 400 mm evaporator, 400 mm condenser and 200 mm adiabatic sections were experimentally investigated in this paper. Experiments were performed by using deionized water and nanofluid that includes bentonite nanoparticles and Sodium Dodecyl Benzene Sulfonate at the rate of 2% and 0.5% (by mass), respectively. During each test, heat pipe was charged with 44.2 ml working fluid and experiments were performed keeping the heat pipe at 90 angle with horizontal under vacuum conditions. 200 W, 300 W and 400 W of heating powers in the evaporator section and 5 g/s, 7.5 g/s and 10 g/s of cooling water mass flow rate in the condenser section were employed for each working fluid. Furthermore, experiments were carried out at different nanoparticle concentrations (0.5%, 2% and 4%) in order to investigate the influences of concentration change on heat pipe performance. An increment of 37% in efficiency of the heat pipe was achieved in the test realized at 200 W heating power and 5 g/s cooling water mass flow rate, when bentonite-containing nanofluid was used as working fluid.