As a part of the U.S.-R.O.C. collaborative deep seismic imaging experiment, six ocean-bottom seismographs (OBSs) were deployed along the 12 12¡¦N parallel west of Hengchun Peninsula and wide-offset seismic signals from a large air-gun array shot over the line were recorded. A preliminary analysis of these data together with those from another OBS to the east of the peninsula reveals that a 11-km thick crustal layer, interpreted to be an extended continental crust of the southern margin of the Chinese mainland, lies under most of the line and dips toward the east at low angle. A complex margin wedge is observed at depth immediate west and underneath the peninsula, which may have resulted from the thick sedimentary layer, quite likely including the basement complex, pushed against the strong backstop provided by the Philippine Sea plate converging form the east.