Photo-induced bleaching of poly-3BCMU film has been studied experimentally. The UV and visible spectra of poly-3BCMU film have been measured before and after bleaching, showing the evidence of the breakage of the polymer backbones. The possibility of developing bleached films has been demonstrated. The importance of oxygen for photo-induced bleaching has been investigated. It has been shown that a photoresist superlayer on poly-3BCMU film prevents oxygen from sufficiently diffusing into the film during bleaching process and hence greatly slows down the process. The potential applications of bleaching process has been discussed as well.