Bonding nature of hydrogen isotopes on the surface of Li2O has been studied with the CRYSTAL92, ab-initio Hartree-Fock calculation code for periodic systems. It was found that the exothermic dissociative adsorption of H2O molecule could occur on the relaxed surface. The adsorption energy for the most stable site was 0.438eV per one H2O. The nature of -OH on the surface of Li2O was also analyzed. Calculation results showed that the stretching vibration of O–H is affected by the chemical species around the -OH.