The present paper addresses the correlation between mechanical damage and the change in electrical resistance of CFRP under tensile loading. A linear relation between the strain and the electrical resistance of single carbon fibers was obtained experimentally, and the electrical behavior of CFRP under tensile loading was investigated. At stresses approaching the failure stress, the composite resistance rises non-linearly, which is attributed to damage in the form of broken fibers. These experiments lead to the concept of electrical ineffective length over which a broken fiber does not carry electric current, in analogy to the well-established mechanical ineffective length over which a broken fiber carries reduced stress. Based on this concept, a DC circuit model consisting of a serial array of discrete parallel cells of length equal to the electrical ineffective length is proposed to explain the resistance evolution in the composite. An analytical model for fiber damage evolution within the electrical ineffective length is constructed using the Global Load Sharing model and the Weibull fiber strength distribution, The model successfully explains the experimental results on the resistance change of CFRP under tensile loading with an electrical ineffective length of 5 mm. (C) 2001 Elsevier Science Ltd. All rights reserved.