This study describes the preparation of a nanocomposites fabricated from monodispersed 4-nn iron oxide (Fe3O4) coated on the surface of carboxylic acid containing multi-walled carbon nanotube (c-MWCNT) and polypyrrole (PPy) by in situ chemical oxidative polymerization. High-resolution transmission electron microscopy images and X-ray diffraction (XRD) data indicate that the resulting Fe3O4 nanoparticles synthesized using the thermal decomposition are close to spherical dots with a particle size about 4 +/- 0.2 nn. The resulting nanoparticles were further mixed with c-MWCNT in an aqueous solution containing with anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate to form one-dimensional Fe3O4 coated c-MWCNT template for further preparation of nanocomposite. Structural and morphological analysis using field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and XRD showed that the fabricated Fe3O4 coated c-MWCNT/PPy nanocomposites are one-dimensional core (Fe3O4 coated c-MWCNT)-shell (PPy) structures. The conductivities of these Fe3O4 coated c-MWCNT/PPy nanocomposites are about four times higher than those of pure PPy matrix.(C) 2008 Wiley Periodicals, Inc.