A unified potentiostat circuit for both O 2 -and H 2 O 2 -based electrochemical glucose sensors was proposed and its function was verified by circuit simulations and measurement results of a fabricated chip. This circuit consisted of an operational amplifier, a comparator and current mirrors. The proposed circuit was fabricated with a 0.13 ㎛ thick oxide CMOS process and an active area of 360 ㎛ × 100 ㎛. The measurements revealed an input operation range from 0.5 V to 1.6 V in the H 2 O 2 -based bio-sensor and from 1.7 V to 2.6 V in the O 2 -based bio-sensor with a supply voltage of 3.3 V. The evaluation results showed that the proposed potentiostat circuit is suitable for measuring the electrochemical cell currents of both O 2 -and H 2 O 2 -based glucose sensors.