An experimental investigation was performed on the thermal performance and heat transfer characteristics of acetone/zirconia nanofluid in a straight (rod) gravity-assisted heat pipe. The heat pipe was fabricated from copper with a diameter of 15 mm, evaporator-condenser length of 100 mm and adiabatic length of 50 mm. The zirconia-acetone nanofluid was prepared at 0.05–0.15% wt. Influence of heat flux applied to the evaporator, filling ratio, tilt angle and mass concentration of nanofluid on the heat transfer coefficient of heat pipe was investigated. Results showed that the use of nanofluid increases the heat transfer coefficient while decreasing the thermal resistance of the heat pipe. However, for the filling ratio and tilt angle values, the heat transfer coefficient initially increases with an increase in both. However, from a specific value, which was 0.65 for filling ratio and 60–65 deg for tilt angle, the heat transfer coefficient was suppressed. This was attributed to the limitation in the internal space of the heat pipe and also the accumulation of working fluid inside the bottom of the heat pipe due to the large tilt angle. Overall, zirconia-acetone showed a great potential to increase the thermal performance of the heat pipe.