This study presents the improvement in heat transfer performance of a heat pipe using silver nanoparticles dispersed in DI (De-Ionized) water. The nanoparticles suspended in conventional fluids have superior heat transfer capability due to improved thermal conductivity. The heat pipes are tested for heat inputs ranging from 20W to 100W in five steps, which is suitable for removing heat from power transistors in electronics and processors in computers. The effect of various operational limits and test parameters such as heat inputs, volume fraction, vapour temperature on the thermal resistance, evaporation and condensation heat transfer coefficients, are experimentally investigated. The tested silver nanoparticles volume concentration ranged from 0.003% to 0.009% with average nanoparticle diameter of 58.35 nm. The experimental results are evaluated in terms of performance metrics by direct measurement of vapour temperatures in the centre core of heat pipe. A substantial reduction in thermal resistance of 76.2% is observed for 0.009 vol.% concentration of silver nanoparticles. Further an enhancement in the evaporation heat transfer coefficient of 52.7% is observed for the same concentration. The use of nanoparticles enhances the operating range of heat pipe by 21% compared with that of DI water. (C) 2012 Elsevier Ltd. All rights reserved.