In this study, the experimental investigation is conducted on the heat transfer characteristics of inclined copper sintered wick heat pipes using surfactant free CuO and Al2O3 nanofluids. The morphology and size of CuO and Al2O3 nanoparticles kept remains same as well as the effects of mass concentrations at an optimum inclination angle of 45° are studied. Interestingly, the addition of nanoparticles in a base fluid reduces the difference between the surface and vapour temperature of the heat pipe. The thermal resistance of the heat pipe has showed a decreasing trend with the inclusion of nanoparticles and their concentration. The reduction in thermal resistance is achieved viz. 20.13%, 49.64% and 28.22%, for CuO nanofluids and 14.55%, 26.07% and 39.67% for Al2O3 nanofluids respectively. The overall thermal conductivity of heat pipe has produced a maximum value of 584.23 W/m°C for CuO nanofluid heat pipe at 1.0 wt.% with 45° inclination. The heat pipe is operated with DI water which produced only 69.08 W/m°C. The thermal efficiency of the heat pipe filled with CuO nanofluid has obtained the maximum performance of 30.42% at the optimum weight fraction of 1.0 wt.%, whereas Al2O3 nanofluid heat pipe reaches its maximum value of 26.17% for the mass concentration of 1.5 wt.%. The thermal performance of heat pipe is enhanced through the addition of nanoparticles which reduced the surface tension of working fluid. Due to this process the solid–liquid wettability has increased. The inclination of the heat pipe has improved the higher on-set of liquid film over the condenser surface area as well as will increase the rate of heat removal in the condenser section. © 2017 Taiwan Institute of Chemical Engineers