The role of new nanofluid based on multi-walled carbon nanotube (MWCNT) on the heat transfer efficiency of a closed loop pulsating heat pipe (CLPHP) has been investigated in this research. For this purpose, surface modification of MWCNT was utilized to prepare uniform and stable nanofluids. Therefore, chemical surface modification and polymer wrapping treatment were conducted on the nanotubes, and then, the thermal conductivity of synthesized nanofluids was measured to investigate the effect of these Nano complexes on the thermal resistance of CLPHP system. In addition, the effect of other CLPHP parameters such as filling ratio, operating pressure and different working fluids were investigated. The results revealed that these nanofluids could enhance the heat transfer coefficient (HTC) of the system by up to 27% when they used as the working fluid in a CLPHP. Furthermore, these experiments indicated that the CLPHP increased the HTC by up to 30% compared to a copper fin that is known for its higher HTC among the metals. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.