1. The absorption maximum on the addition of phosphate buffer after the dissolution of ester-form bilirubin into caustic soda solution dasplayed at 410 mμ imediately after the dissolution without the relation of the pH value of solvent and the diazo reaction showed prompt one. 2. Ester-form bilirubin was rapidly destroyed with high pH value in alkaline solution. The velocity of oxidizing decomposition was more rapid than that of crystalline bilirubin. 3. Bilifuscin obtained from ester-form bilirubin displayed the absorpton maximum at 331 mu by the ester combination, but the proper absorption maximum with the rise of absorption curve tending to the side of short wave length from 280 mμ was not observed. The absorption curve of propentdyopent product did not show the proper absorption maximum, except the absorption maximum of ester combination, but it's absorption maximum displayed at 523 mμ after pentdyopent reaction. 4. Ester-form bilirubin resolved into biliverdin, a product with the complicated small absorption maximum between 612 and 592 mμ and a product with the absorption maximum at 400 mμ by the oxidation of oxygan, and it turned to bilifuscin through pentdyopent product on the further oxidation. 5. Bilirubin and biliverdin were identified by chromatography in alkaline solution of ester-form bilirubin after the disappearance of it's absorption maximum and the display of negative diazo reaction.