The solubility of tritium in Li2O crystals equilibrated with HT-H2 and T2 gas was measured. The solubility of tritium in Li2O was found to obey Sieverts' law. The Sievert's constants Ks for hydrogen and tritium dissolution in Li2O were determined to be log Ks = (1271 ± 46)/T + (2.33 ± 0.07) atm1/2 and log Ks = (1290 ± 81)/T + (1.14 ± 0.11) atm1/2, respectively. The thermal release behavior of tritium dissolved in Li2O crystals resembled that produced in neutron-irradiated ones. But the diffusivity of tritium in the unirradiated crystal was somewhat lower than that of the neutron irradiated crystal. The diffusion coefficient determined in the temperature range from 600 to 711 K was D =1.2 × 10−7exp −(45.1 ± 3.8) × 103[J/mol]/RT cm2/s.