Solvent shift effect on absorption spectra of oxodipyrromethenes and bilirubin IX-${alpha}$ were studied. In methanol or acetic acid the oxodipyrromethenes exist as flat conjugated conformations and in strong acid medium as enol forms of oxodipyrromethenes and bilirubin. The visible absorption bands of bilirubin IX-${alpha}$ and the model compounds, oxodipyrrinethenes, are assigned as ${pi}{ ightarrow}{pi}^{ast}$transition due to their large molar absorption coefficients and to the fact that the more alkyl-substituted one absorbs at rather longer wavelengths than less alkyl-substituted one. A weak blue shift of bilirubin IX-${alpha}$ in polar solvent is probably attribute to disruption of intramolecular hydrogen bond.