Abstract: An experiment was performed to investigate the effect of the inclination angle on thermal performance of screen heat pipe using nanofluid.The study key were the effects of the inclination angle and operating pressure on the heat transfer of both evaporator and condenser as well as the maximum heat flux of the heat pipe.The nanofluid consisted of water and CuO nanoparticles having a mean diameter of 50nm.The concentrations of nanofluid ranged from 0.5wt% to 2.0wt% and the operational pressures of the heat pipe varied from 7.45kPa to 19.97kPa which corresponds to saturated temperature ranged 40℃ to 60℃.The experimental results show that the effect of the particle mass concentration has a significant influence on the heat pipe thermal resistance.There exists an optimal concentration which corresponds to the minimum value of thermal resistance and this optimal concentration is 1% for all inclination angles.The inclination angle also has a very significant effect on the heat transfer enhancement effect for the heat pipe using nanofluid.There exists an optimal inclination angle which corresponds to the maximum enhancement of the thermal performance and this angle is.At the pressure of 7.45kPa,the evaporating heat transfer coefficients can be maximally enhanced about 20%,and the maximum heat flux averagely increased about 25%,while the thermal resistance decreased about 15%,when horizontal tube was replaced by the inclined tube of 45°.