Electrospun polyacrylonitrile (PAN) nanofibers were impregnated with KMnO4 under varying conditions of concentration and time. The morphological structures, chemical and thermal properties were studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The original and preoxidized samples were stabilized and carbonized for characterization with SEM and FTIR. The coloration, weight gain and solubility in N,N-dimethylformamide were also evaluated. A clear peak at 2340 cm(-1) corresponding to MnO4-C=N conjugation, together with a wide peak at 1650 cm(-1), was revealed in the FTIR spectrum of the preoxidized samples. Based on the DSC results, the cyclization reactions in the preoxidized samples were accelerated by initiating the exothermic reaction at lower temperatures. The modified samples had higher reaction times and Delta H values, broad exotherms, lower initial induction time and lower T-i values than the untreated ones.