The electrochemical properties of poly(acrylonitrile)(PAN)/poly(pyrrolexppy) composites prepared by electrochemical polymerization of pyrrole in an insulating PAN matrix were studied. PAN/PPy composite film on platinum electrode could be repeatedly driven between the conductinal and insulating state. Cyclic voltam-movams(CVs) showed that the redox reaction of PAN/PPy composite was not electrochemically reversible and dependent on the nature of the electrolyte used. CVs also showed that the Vonh rate of PPy in PAN matrix was influenced by the polymerization conditions such as the type and the concentration of the electrolyte. The relationship between anodic peak current and scan rate during the potentialcycling indicated that the redox reaction of PAN/PPy composite on platinum electrode was dialsion-controlled reaction.