This paper presents a single-inductor bipolar-input bipolar-output(SIBIBO) DC-DC converter for thermolectric energy harvesting. With an advanced topology, the converter can not only deal with bipolar input voltages but also generate bipolar output voltages. To improve the conversion efficiency, the open-circuit voltage maximum power point tracking method is applied in this design. In addition, a precise VCO is proposed to dynamically adjust the switching frequency according to the input voltage. Designed and simulated in an 180nm CMOS process, the harvester achieves a peak conversion efficiency of 90.3% at VTEG=200mV and 96.9% at VTEG=-190mV .