Hollow Fe3O4-polyaniline (PANI) spheres with uniform cavity size and shell thickness were prepared by an easy and effective approach. In this method, sulfortated polystyrene (PS) spheres were used as templates: aniline was oxidized and polymerized in the shell of sulfonated PS. Since PANI was in situ doped by sulfonic acid, the as-synthesized PANI/PS had good conductivity. Moreover, the resulting PANI/PS layer could adsorb the target precursor, and then formed Fe3O4-PANI/PS composite capsules. Finally, sulfortated PS cores were dissolved and removed from the composite capsules by solvent extract, which resulted in producing hollow Fe3O4-PANI spheres with uniform size. The hollow composite spheres exhibited a superparamagnetic behavior at room temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder scattering (XRD) were applied to characterize the nanocomposite spheres. (c) 2008 Elsevier B.V. All rights reserved