Absorption spectra of N,N-dimethylindoaniline (phenol blue, PB) in supercritical carbon dioxide fluid (SF-CO2) were measured at pressures of 6.8 to 25 MPa and temperatures of 313 to 343 K. The pi-pi* transition energy E-T of PB in SF-CO2 was determined from the wave number at which maximum absorption occurred. The transition energy was found to decrease as pressure increased and temperature decreased. In order to interpret the solubility correlating with CO2 density, the local density around the PB molecule was defined by comparing the experimental E-T With the theoretical transition energy derived from McRae＇s equation using the bulk density of CO2. The solubility determined from the absorption intensity of PB was found to be in good correlation with the estimated local density. The solvation characteristics of CO2 around PB corresponded well with the local density.