Recently, the high voltage DC feeding system has been researched and developed to save electrical energy and to make use of the green energy from the solar cell, wind turbine and so forth. This paper presents a novel high efficiency DC-DC converter for isolation in high voltage DC feeding systems. The prototype 4.0kW bidirectional DC-DC converter has been made and tested. As a result, in the forward and regenerative operation modes, the maximum power efficiency over is 98.4% and the regulation degree of the output voltage is within 2% under the output power condition from 0.1kW to 4.0kW.