We have prepared polyacrylonitrile (PAN) thin films containing Au nanoparticles by heat treatment of Au/PAN stacking films. The effect of heat treatment on the microstructure of the composite films was investigated by means of transmittance electron microscopy (TEM), Fourier-transform infrared (FT-IR) and Raman spectroscopy. The Au nanoparticles initially deposited on the PAN film were found to be dispersed into the PAN layer by heat treatment at 200 degreesC after which structural changes in the PAN matrix were observed, i.e. decomposition of methylene and nitrile groups into C=N conjugation. It was also found that heat treatment of the films at higher temperatures caused change of the PAN matrix into amorphous carbon. The mean size of the Au nanoparticles increased with increasing heat-treatment temperature.