Low DC-DC converter(LDC) in HEV plays a role in charging the auxiliary battery as a low voltage from the main battery charged to the electric driving motor"s regenerative energy during deceleration and braking of the vehicle. The charged auxiliary battery supplies power to the electronics such as headlamps, air conditioner, power windows, and electric power steering. LDC"s output of degradation and failure in the vehicle can have severe impact on various electronics during driving. LDCs for HEVs compared to general industrial DC-DC converters need to meet the performance of high-efficiency power conversion, vibration, and heat resistance properties and EMI to ensure the reliability within the limited volume to be mounted in the vehicle. In this paper, reliability assessment and performance evaluation factor are established for developing the LDC in HEV. Also the performance testing and analysis about the conventional LDC currently used in a HEV is performed on the status of the vehicle and device. The result will be uesd to compare the developed LDC"s performance.