Polyacrylonitrile (PAN) nanofibers as a precursor of carbon nanofibers with diameters in the range of 130-280 nm were obtained by electrospinning of PAN/DMF solution. Morphologies and structures of PAN precursors were investigated by scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), infrared spectrometer (IR) and differential scanning calorimeter (DSC). Distribution of diameters of PAN precursor showed log normal distribution. Molecular chains were oriented within the electrospun fibers during the electrospinning process. The cyclization exothermic peak shifted to lower temperature for electrospun nanofibers, which suggested that cyclization was more easily initiated at lower temperature for electrospun nanofibers. (C) 2005 Elsevier B.V. All rights reserved.