An in situ polymerization route has been developed to synthesize SiO2/polypyrrole core-shell particles and polypyrrole hollow spheres with controllable shell thickness. In this process, pyrrole monomers adsorbed on the surface of SiO2 spheres due to electrostatic interactions, SiO2/polypyrrole core-shell particles could be subsequently obtained in large quantities via in situ polymerization under hydrothermal conditions. Furthermore, polypyrrole hollow spheres could be obtained after the removal of the core via HF etched method. The shell thickness of core-shell particles and hollow spheres could be easily controlled by adjusting the process parameters such as monomer concentration and hydrothermal temperature. The morphology, size and structure of the final products were investigated in detail by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier-transform infrared spectra (FTIR). The probable formation mechanism of core-shell particles and hollow spheres was proposed on the basis of the experimental results. (C) 2007 Elsevier B.V. All rights reserved.