Conducting polymers such as poly(p-phenylene vinylene) (PPV) can serve as the active material in sensor devices because PPV possesses good optical and electrical properties, and it can be synthesized by a relatively simple technique. Our objective is to develop an analyte-specific material; the sensors should have very broad chemical specificity with high sensitivity towards polar chemicals. In order to achieve this objective, a zeolite is chosen as a selective microporous adsorbent to be introduced into a polymer matrix in order to increase sensitivity of our CO sensors. This work will report on the effects of zeolite type, Si/Al ratio of zeolite, and cation type on the electrical responses of various composites when exposed to CO.