A single-inductor bipolar-output (SIBO) DC-DC converter was designed for the application of neural stimulation was proposed, featuring with high light-load efficiency and low design complexity. The proposed SIBO system generated both positive and negative voltages in the same time by using only one inductor and two-phase control rhythm, which greatly reduced the complexity of the control logic, and improved the efficiency. Constant on-time (COT) control was applied to improve light-load efficiency. The proposed SIBO system was powered by a single-cell lithium battery with an input voltage range of 3 V to 4.2 V. The output voltage of ±16 V, ±12 V, ±8 V, or ±4 V were enabled in different modes. Output voltage ripples of 4.5 mV of VOP and 3.4 mV of VON were achieved with a ±16 V output voltage and a 1 mA load current according to post simulation. A maximum power efficiency of 94.8% was achieved with a 1.3 mA load current. The circuit featured high efficiency, small output voltage ripple and low design complexity.