The present study conducted two different structures, namely raw and acid oxidized multi-walled carbon nanotubes (MWCNTs) were ground under wet condition at various rotation speeds (300-600 rpm). The ground MWCNTs were dispersed in aqueous solution by ultrasonication was investigated. The particle size analyzer reveals the agglomerated size of raw MWCNTs ground at a rotation speed of 300 rpm was 69.2 mu m. Nevertheless, the agglomerated size of particle significantly decreased to 13.2 mu m after grinding at a rotation speed of 600 rpm. The maximum absorbance (4.0 abs at a wavelength of 300 nm) and highest thermal conductivity enhancement (18.12% at 40 degrees C) of suspensions correspond to the grinding speed of 600 rpm assisted by ultrasonication dispersion of the purified and raw structures, respectively. It is found that the grinding method with high rotation speed plays can be significantly increased both the dispersibility and thermal conductivity of raw and purified MWCNTs nanofluids. (C) 2012 Elsevier Ltd. All rights reserved.