Observing the infrared absorption spectra of these both biliverdins, L. Light company made and the refined one (Part 1), after adding caustic soda slightly more than the calculated amount and decicated by vacum sactioning in room temperature, and the following results were obtained. 1) In the absorption band of L. Light company made biliverdin, C=O streching vibration of the carbonyl group (γ C=O) at 5.82 μ and a broad absorption band ranging over 5.90 μ to 6.46 μ. was seen instead of 5.86 μ to 6.04 μ. which was thought to be of the ionized carboxyl group. 2) In the absorption band of the refined biliverdin, no C=O streching vibration of the carbonyl group (γ C=O) at 5.88 μ., and the absorption band of the ionized carboxyl group was seen at 6.20-6.40 μ., which was probably due to sodium salt formation. 3) In the refined biliverdin the perfect sodium salt formation was observed following the addition of caustic soda, on the other hand, it was imperfect in the L. Light company made biliverdin, probably due to impurity of the biliverdin itself. Therefore, some corrections would be necesseary for the Shindo's result in his experiment about this study.