Mesoporous silica SBA-15 with conducting polyaniline inside the pore channels was synthesized and nanocomposite formation was confirmed by means of X-ray diffraction, transmission electron microscopy and via an N-2 adsorption isotherm. The nanocomposite was subsequently used as a dispersed phase in electrorheological (ER) fluids, and the ER effect has been demonstrated for the first time using a rotational rheometer with high voltage generator.