Novel core-sheath nanofibers, composed of polyacrylonitrile (PAN) core and polypyrrole (PPy) sheath with clear boundary between them, were fabricated by electrospinning PAN/FeCl3 6H(2)O bicomponent nanofibers and the subsequent surface-initiated polymerization in a pyrrole-containing solution By adjusting the concentration of FeCl3 6H(2)O, the surface morphology of PPy sheath changed from isolated agglomerates or clusters to relatively uniform thin-film structure Thermal properties of PAN-PPy core-sheath nanofibers were also characterized Results indicated that the PPy sheath played a role of inhibitor and retarded the complex chemical reactions of PAN during the carbonization process (C) 2010 Elsevier Ltd All rights reserved