Electrically conductive fibers have been prepared by polymerization of pyrrole on surfaces of commercial polymer fibers. Thickness and morphology of the conducting thin film on the surface of the fibers were examined by scanning probe microscopy, indicating a strong dependence of the substrate's nature, in addition to the processing conditions. Electromechanical property was investigated by an electromechanical testing system, showing that a smooth and uniform coating and the matched mechanical properties will lead to a satisfied performance of conductive fiber sensors. The difference in the behavior of two types of composite fibers was investigated by scanning electron microscopy in situ observations. (c) 2005 Wiley Periodicals, Inc.