Semi-conductive membranes from poly(vinylidene fluoride)/polyaniline (PVDF/PANi) blends in N-methyl-2-pyrrolidone (NMP) solution were prepared by phase inversion in an aqueous solution of poly(styrenesulfonic acid) (PSSA). Entrapment of a "stoichiometric" amount of PSSA dopant molecules (with respect to the PANi content) into the membrane occurred during the phase inversion process and gave rise to a semi-conductivity membrane. The PSSA-doped (protonated) PVDF/PANi blend membranes were studied by FT-IR spectroscopy, UV-visible absorption spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the PANi and PSSA chains dispersed uniformly in the doped PVDF/PANi blend membranes. The morphology of the membranes was studied by scanning electron microscope (SEM). The membrane was found to have an asymmetry structure with a dense skin layer and a porous inner layer. The membrane exhibited excellent stability in doping/protonation level (and thus conductivity), even after prolonged exposures to an aqueous medium, as revealed by XPS and surface resistance measurements. (C) 2002 Elsevier Science B.V. All rights reserved.