A core-shell structured electro-responsive electrorheological (ER) particle system comprised of monodisperse poly(2-methylaniline)-coated polystyrene (PS/PMAN) microspheres was fabricated by applying a controlled swelling-releasing technique to pre-fabricated micron-sized PS seeds using a dispersion polymerization method. Compact wrapping of the PS microparticles with semiconducting PMAN without a de-doping process was examined by scanning electron microscopy and transmission electron microscopy. Fourier-transform infrared spectroscopy and thermogravimetric analysis also confirmed the chemical composition and thermal stability of the particles, respectively. Rheological characteristics of the PS/PMAN microsphere based ER fluid dispersed in silicone oil at various electric field strengths revealed a typical ER response under both steady shear flow and dynamic oscillation, demonstrating its mechanism of a conductivity model with a slope of 1.5. (C) 2014 Elsevier Inc. All rights reserved.