Fluid inclusions in olivine were extracted in vacuum by a sodium carbonate fusion method. In the present study, bulk hydrogen content and D/H ratio of the inclusion were measured. The results showed that a consistent value of δD was obtained with a standard deviation of ±2‰, when the absolute amount of hydrogen extracted was more than 40μmol (0.9ml STP H₂). On the other hand, when the absolute amount of extracted hydrogen was less than 40μmol, δD value of the extract fluctuated, probably being affected by the contamination in the whole procedure.