Polyaniline co-doped with titanium ions and protonic acid was synthesized in aqueous H2SO4 solution containing Ti(SO4)(2) (pH 2), and was characterized via Fourier-transform infrared spectra, UV-vis spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and cyclic voltammetry. Its conductivity was 2.8 S cm(-1) at room temperature (25 degrees C), which is the same order of magnitude as polyaniline doped with protonic acid (5 S cm(-1)). Compared with polyaniline doped with protonic acid, it showed a better redox reversibility and cycling stability in aqueous pH 4.0 media, even in an acetate electrolyte (pH 4.0). It could be a promising material for several applications due the increase of the operating pH window of polyaniline in an aqueous environment. (C) 2009 Elsevier Ltd. All rights reserved.