Atomic force microscopy (AFM) has been used to characterize the modification of the large-scale surface morphology of thin films of electropolymerized polyacrylonitrile (PAN) before and after rapid thermal treatment (RTT) at different temperatures. This study was led together with infrared spectroscopy investigations which provide information about the evolution of the chemical structure of the heated polymer samples. The results bring invaluable clues on how surface changes resulting from RTT occur. For the softest heat treatments. the : melting of the polymer clearly leads to a significant leveling of its extreme surface : for the strongest ones, the chemical evolution of the layer is probably accompanied by the release of gaseous products which increases the microroughness of the film.