Abstract Polystyrene/polyaniline (PS/PANI) composites were prepared by emulsion polymerization of aniline in a mixture of PS and dichloromethane, at different feeding ratios of aniline to PS. Dodecylbenzenesulfonic acid (DBSA) was used as a dopant during chemical oxidation of aniline. Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD), scanning and transmission electron microscopies (SEM and TEM) were used for structural characterization of the composites. The effect of PANI content on electrical properties of the composites was studied by electrical resistivity and electromagnetic interference (EMI) shielding measurements. Electron microscopy showed that the conductive PANI distributed in the continuous PS matrix, heterogeneously. Electrical conductivity, EMI shielding effectiveness, real permittivity and imaginary permittivity values increased with PANI content. It was found that absorption had more contribution to EMI shielding than reflection. 1.1 mm thick samples of the composites exhibited electrical conductivity up to 10−2 S/cm and electromagnetic interference shielding effectiveness (EMI SE) up to 8 dB, for sample containing ca. 20 wt% PANI.