This chapter describes a new approach of on-line structural health monitoring using fibrous sensors inserted inside textile composite reinforcements is presented. Prior to insertion in the carbon fiber reinforcement, the sensor should be coated with an insulating layer. This is because of the fact that the carbon multifilament tows used for weaving of composite reinforcement are conductive and may disturb the functioning of the piezoresistive fibrous sensor. As coating solution for our sensors, a conductive polymer composite based on dispersion of carbon black particles in polymer solution, using chloroform as a solvent was chosen. In order to characterize the sensitivity and adherence of the coating on different substrates, the carbon black solution was coated on different yarns. The electrical resistivity of the carbon black coating is supposed to be homogeneous as the conductive charges are uniformly distributed over the surface of the substrate.