A neutron powder diffraction study was performed to determine the sites occupied by hydrogen in the structure of DHMS phase G, which is stable at the pressure-temperature conditions of the transition zone and lower mantle. The diffraction data from small samples (about 3 mg) were collected by using a highly sensitive imaging plate detector at the BIX-3 beamline at JRR-3M nuclear plant in JAERI Tokai Laboratory, Japan. The present neutron diffraction data reveal that hydrogen (and deuterium) is located in the 6k site of Wykoff letter in the MO6 layer of the phase G structure with the space groupP3¿1m. The bond lengths of O-H and O-D are 1.1(4) and 0.8(3) ¿, respectively. This result is consistent with previous Raman spectroscopic studies of this phase. ¿ 2001 American Geophysical Union