Silica or titania uniformly coated multi-walled carbon nanotubes (MWNTs) were fabricated using the tetraethyl orthosilicate (TEOS) or titanium butoxide (TBT) for the application of electrorheological (ER) fluids. The electrorheological and dielectric properties of the two different core/shell nano-tube based ER fluids were measured using rheometer and impedance analyzer. The titania-coated MWNTs ER fluids have shown higher static yield stress as well as dynamic viscoelastic properties compared to the silica-coated MWNTs ER fluids under external electric field. The silica or titania-coated MWNTs ER fluids have shown high permittivity and short relaxation time of interfacial polarization in the dielectric spectra measurement. It was found that the permittivity and electrical conductivity of the MWNTs can be controlled by coating with either the silica or titania onto the functionalized MWNTs. (C) 2013 Elsevier B.V. All rights reserved.