Seismic, sonic logging and geothermal data are analyzed to show the distribution of gas hydrates in the Dongsha region north of the South China Sea. Bottom simulating reflectors (BSRs) and amplitude blanking zones are revealed in seismic profiles. A high velocity interval and a velocity reverse are distinguished by sonic logging.The BSR depth is compared with thickness of gas hydrate stability zone from geothermal gradient data. The BSR at ODP sites 1144 and 1148 occur at 654 and 475 meters below sea floor respectively. The top of the amplitude blanking zone may be related to gas hydrate bearing strate in a region adjacent to ODP site 1144, at about 450 meters below the sea floor.