Laser ablation of Upilex-S polyimide films 80 mum thick was performed in air using a pulse TEA CO, laser with wavelength 9.3 mum. A halo surrounding the hole was observed, which is covered with sub-micro particles. Pieces of ablation products protrude from the ablated surface, leading to considerable roughness of the ablated area. Chemical and structural changes of Upilex-S polyimide film surface irradiated by the pulse TEA CO, laser in air were analyzed by X-ray photoelectron spectroscopy (XPS). Relative C content in the ablated area was found to be higher, whilst both O and N contents were lower than in the untreated area. This means that TEA CO2 laser ablation released both the O and N atoms. Also, the peak areas corresponding with carbonyl group (C=O) in the imide system were reduced much more and a new component at 287.0 eV assigned to the amide structure (N-C=O) was detected after laser ablation. These suggest that the pyrolysis of the Upilex-S polyimide was the decomposition of the imide ring between the nitrogenlaromatic carbon atom and carbonyl carbon atom- In addition, another new component arising from >C=O groups was also detected for higher fluence (7.83 J/cm(2)), and its peak areas is very small. This result indicates that the slight oxidation may take place with higher fluence, during laser ablation in air. Based on above-mentioned experimental results, a possible thermally-induced decomposition path of Upilex-S polyimide ablated by TEA CO2 laser is presented.