Micron-sized PANI beads with a porous sea urchin like appearance, mean diameter of 2.5 mu m and spherical shape, were synthesized by a self-assembly process from PANI nanowires. The nanowires were polymerized using ammonium persulfate as an oxidant in an aqueous solution. The structure of the urchin-like PANI microspheres was characterized by scanning electron microscopy, while the Brunauer-Emmett-Teller specific surface area of the urchin-like PANI microspheres was calculated from N-2 adsorption/desorption. The microspheres, which were dedoped to a low conductivity, were then applied to electro-responsive electrorheological (ER) materials dispersed in silicone oil with a volume fraction of 10%. The particulate structures of the ER fluid under an applied electric field were observed by optical microscopy. The ER properties of the ER fluid including the shear stress, shear viscosity and yield stress were examined using a rotational rheometer under an applied electric field. (C) 2013 Elsevier B.V. All rights reserved.