Ultratine fibers were spun from polyacrylonitrile (PAN)/N,N-dimethyl formamide (DMF) precursor solution using a homemade electrospinning setup, and then pyrolyzed in vacuum at 873, 1073, 1273 and 1473 K, respectively. The pyrolyzed fibers, with diameter of the order of 100 nm as revealed by a scanning electron microscope (SEM), were characterized using Raman microspectrometry. Their Raman scattering spectra manifested D and G peaks, characteristic of disordered carbon and graphite, respectively. The D and G peak parameters were fitted using a Gaussian-Lorentzian mixed shape, and graphitic crystallite size and mole fraction in the nanofibers were estimated from the ratio of the integrated intensity of D and G peaks. The graphite domain size was found to be between 1.5 and 2.6 nm, increasing with the pyrolyzing temperature. The graphite mole fraction was found to obey an Arrhenius relation with the pyrolyzing temperature. with the graphitization activation energy of 7.36 +/- 0.11 kJ/mol. (C) 2002 Elsevier Science B.V. All rights reserved.