Abstract: This paper describes that the absorption spectrum of bilirubin solution was changed. obviously by photo-oxidation. The absorbance was measured at 453 nm before and after light irradiation. The contents of bilirubin of ox gallstone in Liuying pills, Liushen pills and Niuhuang Xiaoyan pills were determined by differential absorbance (AA). Calibration graph was linear in the range of 1.6～8.0μg/ml for ΔA. The average recoveries for three Chinese patent medicines were over 93%. Determinations of bilirubin in Chinese patent medicines were not affected by other components.