The excitation energies of O-3-H2O complex have been calculated by means of SAC-Cl method to elucidate the spectral shifts of excitation energies of O-3 caused by the complex formation with a water molecule. The eclipsed form, where the center oxygen of O-3 and water oxygen are located on the C, molecular plane, was examined in the present study. The first and third excitation energies of O-3 were slightly blue-shifted by the complex formation with H2O. The oscillator strength for the third excitation was not affected by the complex formation, indicating that the photo-dissociation of the O-3-H2O Complex occurs efficiently as well as free ozone molecule. The electronic states of the complex was discussed on the basis of theoretical results. (c) 2006 Elsevier B.V. All rights reserved.