This article studied experimentally the effect of multi-wall carbon nanotubes (MWCNTs) on the thermo physical properties of ionic liquid-based nanofluids. The nanofluids were composed of ionic liquid, 1-ethyl-3-methylimidazolium diethylphosphate [EMIM][DEP], or its aqueous solution[EMIM][DEP](1) + H2O(2) and MWCNTs without any surfactants. The thermal conductivity, viscosity and density of the nanofluids were measured experimentally. The effects of the mass fraction of MWCNTs, temperature and the mole fraction of water on the thermo physical properties of nanofluids were studied. Results show that the thermal conductivity of nanofluids increases within the range of 1.3%-9.7% compared to their base liquids, and have a well linear dependence on temperature. The viscosity and density of the nanofluids exhibit a remarkable increase compared with those of the base liquids. Finally, the correlation of the effective thermal conductivity and viscosity of the nanofluids was made using the models in the literatures. (c) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.