We have developed a simple hydrothermal route to prepare the necklace-shaped superstructures self-assembled by magnetite (Fe3O4) nanoparticles coated with poly (vinyl pyrrolidone) (PVP). The as-prepared samples were characterized by means of X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) spectra, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermal gravimetric analysis (TGA), magnetic hysteresis loop, and cyclic voltammetry. Magnetic measurement results reveal that the necklace-shaped superstructures show smaller magnetization compared with those of randomly distributed magnetite nanoparticles obtained in the absence of PVR The electrochemical characterization was carried out by cyclic voltammetry, which indicates that the Fe3O4 sample in 1 mol L-1 Na2SO3 aqueous electrolyte is of an excellent electrode material for supercapacitor at the scan rate of 2 mV S-1 in the range of -1.0 to 0.2 V. (C) 2008 Elsevier B.V. All rights reserved.