Surface charged iron oxide (Fe3O4) nanoparticles were used for the synthesis of sulfonated polyaniline (SPAN)-Fe3O4 nanocomposites (SPAN/Fe3O4-NCs). 2,5-diaminobenzenesulfonic acid (DABSA) and 2-amino-benzenesulfonic acid (ABSA) were independently polymerized with aniline to form SPAN. The structure of the composites was characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, conductivity and magnetic properties. ITEM reveals that Fe3O4 nanoparticles are "glued" with SPAN in the composite. TGA indicates that SPAN/Fe3O4-NCs are having better thermal stability. The room temperature conductivity of SPAN/Fe3O4-NCs is higher than that of pristine PANT and SPAN. SPAN/Fe3O4-NCs exhibits magnetic behavior. (c) 2007 Wiley Periodicals, Inc.