Conducting polymeric polyaniline hollow spheres (PANI-HS) were fabricated and evaluated as a smart electro-stimuli responsive material, whose both special structure of shorter diffusion length promotes the electron transfer and specific surface area is greatly amplified than solid spheres. The monodisperse polystyrene (PS) seeds were initially synthesized by a facile surfactant-free emulsion polymerization, and then the monomer aniline was adsorbed and polymerized on the sulfonated PS spheres to form the PS/polyaniline (PANI) composites, allowing the PS cores to be removed by a solvent extraction later. The morphology and shell thickness were examined using both scanning electron microscopy and transmission electron microscopy. Fourier transformation infrared spectroscopy affirmed chemical structure of pure PS, PS/PANI and PANI-HS. The dielectric spectra were further analyzed for their electrorheological (ER) characteristics with LCR meter. The homogeneous semi-conducting PANI-HS based ER fluid (10 vol%) exhibited typical ER characteristics according with the conductivity model based on a slope of 1.5. (C) 2018 Elsevier Ltd. All rights reserved.