Absorption spectra in the amorphous phase consisting of Ir(ppy) 3 and 4,4-bis(carbazol-9-yl)-2,2-biphenyl (CBP) molecules were theoretically investigated. The equilibrium structures in amorphous phase were simulated by QM/MM MD calculations. The results of calculation suggest that eleven CBP molecules exist as the closest neighbors of Ir(ppy) 3 . Time-dependent density functional theory (TD-DFT) calculations successfully reproduced the experimental absorption spectra. For Ir(ppy) 3 in the gas phase, the most important spectral peak at the wavelength of 400 nm can be assigned principally to the one-electron excitation from HOMO-1 to LUMO?2, where the main component of HOMO-1 is the d orbital of the Ir atom and that of LUMO?2 is the p* orbital of the ligands. When Ir(ppy) 3 strongly interacts with a CBP molecule, the p* orbital of the ligand is delocalized into the CBP molecule. This is the reason why the spectral peak at the wavelength of 400 nm almost disappears in the amorphous phase.