A conducting polyaniline (PANI) was synthesized via an oxidative dispersion polymerization technique, using poly(vinyl alcohol) (PVA) as a polymeric stabilizer, in the presence of multi-walled carbon nanotubes (MWNT) purified in acidic solution, and dispersion stability of the MWNT in an aqueous solution of PVA was studied for different PVA concentrations. Their morphology was confirmed by a scanning electron microscope. Its electrorheological (ER) characteristics were also investigated by dispersing the PANI/MWNT composite particles in an insulating silicone oil. Its ER properties were examined using a rotational rheometer under varying applied DC electric field strengths, in which the ER fluid is generally composed of a suspension of conducting particles dispersed in an insulating fluid, which shows a rapid and reversible change in shear viscosity with an applied electric field. Synthesized PANI/MWNT composite particles are observed to enhance interparticular interactions, since the degree of polarization of PANI/MWNT composite particle increases with applied electric field strengths. The shear stresses of the PANI/MWNT nanocomposite based ER fluid increase with the electric field strength for a broad range of shear rates. (c) 2006 Elsevier B.V. All rights reserved.