Changes in refractive index and in film thickness caused by synchrotron radiation are studied in a fluorinated polyimide (6FDA/TFDB). The index at 589.6 nm increased by 1.3% and the thickness decreased by 0.69% for 8-mu m-thick film after 30 min irradiation. X-ray photoelectron spectroscopy analysis was performed on the modified surfaces after synchrotron radiation exposure. From the present data the synchrotron radiation leads to production of a fluorine-poor surface.