By means of the "Swelling-Diffusion-Interfacial-Polymerization Method" (SDIPM), we successfully coated polyaniline (PANi) onto micrometre-size, uncharged polystyrene (PS) particles, which were synthesized by dispersion polymerization. After initially forming aniline-swollen PS particles, diffusion of the aniline toward the aqueous phase was controlled through a slow addition of hydrochloric acid, eventually leading to its polymerization on the substrate particle surface. The resultant PS/PANi composite particles have been extensively characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR) and Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and C, H. and N elemental microanalysis. At very low aniline/PS weight ratio, the thin, uniform, but intact PANi overlayer was obtained owing to its unique "inside-out" formation mechanism and considerably high efficiency of aniline to transform into the resultant composites. As increasing the initial amount of addition of aniline, the uniform size and well-defined morphology of the PS/PANi core-shell composite particles could still be maintained with a relatively high PANi mass loading yield. (C) 2010 Elsevier Ltd. All rights reserved.