This paper focuses on an adaptive interface circuit for polymer-based gas sensors. The sensors use polymer-carbon black composites, which swell reversibly and create resistance change upon exposure to chemical vapors. The initial resistances of sensors are influenced by temperature or humidity. Therefore, an adaptive interface circuit is proposed to cancel baseline signals. The circuit is implemented in a TSMC 0.18um CMOS process and dissipates 49.4uW and operates in 1V. The range of adaptive sensor resistance is 15kΩ to a few MΩ. If the adaptive sensor resistance is set under 110kΩ, the power consumption will allow a portable and lasting electronic nose system.