The adsorption behavior of H2O on Li2O surface was studied by ultra violet photo electron spectroscopy (UPS). Valence-band spectra of Li2O single crystal which was exposed to different pressures of H2O vapor were recorded. After exposure of H2O, variation of the spectra was observed. The observed spectra were interpreted on the basis of ab-initio quantum chemical calculation of the electronic structure of Li2O surface which was covered with –OH. The adsorbate-induced features were assigned as the orbital of surface –OH. The surface condition was varied by Ar ion sputtering and heat treatment under D2 gas. The difference of adsorption behavior of H2O in the surface condition was discussed.