Photodegradation of a photosensitive polyimide containing simultaneously imidosulfonate group and cyclobutane rings in the main chain was investigated by spectroscopic methods such as FT-IR, NMR, and GC-MS. The polyimide underwent a phl,ru-induced decomposition through the cleavage of N-O bund as well as cyclobutane ring, affording maleimide as a photoproduct. The polyimide exhibited enhanced photosensitivity compared to conventional cyclobutane-containing polyimides.