Abstract: Three kinds of ion-pair complexes as electric active materials for making drug sensor have been studied. The active materials were coated on Pt draw wire of MOS-FET to make general local anaesthetic-SFET. Its performance is characterized both as a solid-state field effect device and as an electrochemical sensor. It is one kind of multi-purpose probe which can respond to procaine, lidocaine and dicaine. This device has the advantage of fast response, small size, good stability and can be used for the determination of local anaesthetic materials and their preparations.