The loop thermosiphon for high temperature oil cooling is a high-performance cooling heat exchanger capable of rapidly cooling high-temperature oil by transferring a large amount of thermal energy through boiling and condensation of the working fluid even with a small temperature difference. The loop thermosyphon for high-temperature oil cooling consists of an evaporation unit, an insulation unit, and a condensing section. A 3D simulation and experimental studiss were conducted simultaneously. In this study, the size of the loop thermosyphon for oil cooling is 500mm wide, 70mm long, and 1,100mm high. In addition, the size of the heat transfer tubes of the heat exchanger is 15 mm in diameter and 1,000 mm in length, and 98 heat transfer tubes were installed. The inside of the condensing unit was constructed with heat transfer tubes equipped with high-efficiency insert devices to increase the heat transfer surface area of the heating medium in the heat transfer tubes and low fin shapes were enchased on the outside of the heat transfer tubes with form rolling to increase the heat transfer surface area in contact the fluid inside the cylinder. R134a refrigerant was used as the working fluid of the loop thermosyphon to experiment changes in the temperature of the cooling air outside the condensing unit and the temperature of the refrigerant, and heat transfer performance in relation to mass flow changes and the experimental results were compared with the results of the 3D simulation. According to the results of this study, the rate of transfer of the thermal energy supplied by the evaporation unit of the loop thermosyphon heat exchanger for high-temperature oil cooling and the rate of transfer of the thermal energy absorbed by the air in the condensing unit matched well within the range of ±5%. Therefore, the reliability of the experimental results of this study was verified. In addition, thanks to the heat transfer tubes equipped with high-efficiency insert fins installed inside the condensing unit of the loop thermosiphon for high temperature oil cooling, the condensation heat transfer performance of the condensing unit increased significantly compared to that of condensing units made with flat plates.