The degradation of PI film irradiated with VUV in a wavelength of 5 to 200 nm is investigated. The results show that transparency of PI film decreases obviously after irradiation and more obviously for the film irradiated with VUV of higher intensity. In addition, the absorption line red-shifts for the PI film. The XPS and FTIR analyses results indicate that decarbonylation and the condensation of the benzene group take place under the irradiation and that carbonification takes place under 100 VUV suns. The change of optical property could be attributed to the stabilizing of the conjugation group and as well as to the carbonification to some extent. The character of kVUV on polymer degradation is discussed. (C) 2004 Wiley Periodicals, Inc.