Multi-walled carbon nanotubes (CNTs) were treated by using rnechanochemical reaction method to enhance their dispersibility for producing CNT nanofluids. The thermal conductivity was measured by a short hot wire technique and the viscosity was measured by a rotary viscometer. The thermal conductivity enhancement reaches up to 17.5% at volume fraction of 0.01 for an ethylene glycol based nanofluid. Temperature has no obvious effects on thermal conductivity enhancement for the as prepared nanofluids. With an increase in thermal conductivity of the base fluid, the thermal conductivity enhancement of a nanofluid decreases. At low volume fractions (<0.4 vol%), nanofluids have lower viscosity than corresponding base fluid due to lubricative effect of nanoparticles. When the Volume fraction is higher than 0.4 vol%, the viscosity increases with nanoparticle loadings. The prepared nanofluids, with no contamination to medium, good fluidity, stability, and high thermal conductivity, would have potential applications as coolants in advanced thermal systems. (C) 2008 Elsevier B.V. All rights reserved.