The investigation of the dam foundation structure, the leakage of reservoir bed and dam body is very important factor for the quality and safety of the water reservoir. Earth resistivity tomography, which is a non-destructive method, has been used widely in geo-engineering investigation. This paper contains the results of applying the earth resistivity tomography method in the investigation of dam foundation structures. reservoir beds and embankment dams. It presents three case studies oil applying the earth resistivity tomography to investigate Tan Giang II dam foundation structure in Ninh Thuan province, the fractures/faults, karts possibly causing leakage in the Chieng Co reservoir in Son La province; the actual leakage through the Khuan Cat ernbankment dam in Lang Son province and the quality of its treatment. The investigation results affirm the efficiency of the earth resistivity tomography method in the gee-engineering investigation of reservoirs and monitoring the embankment dams in Vietnam.