The effect of ferric (Fe3+) ion incorporation on the thermal stabilization of polyacrylonitrile (PAN) fibers was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction analysis and infrared spectroscopy methods. The results obtained from the DSC and TGA measurements indicated that there was an improvement in thermal stability when Fe3+ ions were incorporated into the polymer structure. TGA thermograms showed a relative improvement in thermal stability as indicated by increasing carbon yield with progressing time. The degree of lateral order and apparent crystallite size estimated by X-ray diffraction decreased with increasing stabilization time. Incorporation of Fe3+ induced distinct changes in the infrared spectra of the thermally stabilized PAN fibers. The spectral changes appeared to be due to the formation of coordination bonds between the nitrogen atom of the nitrile group and Fe3+. The formation of ferric ion-nitrile coordination bonds accelerated thermal stabilization by catalyzing the occurrence of dehydrogenation, cyclization and oxidation reactions.