Heat transfer enhancement of a heat pipe using aqueous clinoptilolite nanofluid as the working fluid under different operating conditions was studied experimentally and numerically. A thermosiphon-type heat pipe made of copper and is of 13 mm inner and 15 mm outer diameter was used in experiments. The heat pipe performance was investigated by utilizing two different working fluids, deionized water and aqueous clinoptilolite nanofluid. It was charged with a working fluid by one-third of the overall heat pipe volume for each experiments. Experimental study was conducted under three different heat loads and cooling water mass flow rates applied to evaporator and condenser sections of the heat pipe, respectively. Alterations in wall temperature, efficiency and the thermal resistance values of the heat pipe were determined for deionized water and aqueous clinoptilolite nanofluid from the experiments. The maximum heat transfer enhancement and the improvement in thermal resistance of the heat pipe were obtained as 9.63% and 26.31%, respectively, when aqueous clinoptilolite nanofluid was used as working fluid. By means of Computational Fluid Dynamics approach, in addition, a series of numerical study was carried out employing experimental findings and then results from both were compared to each other. As a conclusion, it was seen that experimental and numerical findings were in agreement to each other.