In-situ tritium release behavior from Li2O powder has been investigated under neutron irradiation at high temperatures. It was found that the chemical form of the released tritium depended strongly on the experimental conditions such as pre-treatment (dehumidification) of the sample and the H2 addition to the sweep gas of helium. Water-soluble component was observed to be a main species from the sample pre-dried in N2 stream at 800°C for 3 days, while water-insoluble component had fairly large proportion on the sample pre-dried for 5 days. In the case of He-4%H2 sweep gas, more than 90% of released tritium was water-insoluble even for the sample pre-dried for 3 days. Tritium recovery rate was also accelerated by H2 addition. These experimental results showed that the oxygen activity of the experimental system essentially affected to tritium release behavior from Li2O sample.