<p>In situ stress sensing and damage monitoring of carbon fiber plain-woven composites during service time are critical for their structural health and safety. Here we investigate the electromechanical response of plain-woven composites under static and cycle varied load that are accompanied with the record of real-time electrical resistance change. A four-probe method with the electrical current and voltage measurement is presented. Experimental observations show the electrical resistance changes have a significant relationship with internal damage in plain-woven composites. The elastic elongation, delamination, and yarn fracture are associated with resistance increases, oscillations, and jumps, respectively. The composite samples exhibit long-term stability and repeatability under elastic cyclic loading and high sensitivity under plastic loading which are important for structural health monitoring. As a result, the potential of carbon fiber plain-woven composites to be treated as damage detection and stress sensors is demonstrated without any need for additional sensing elements. It indicates that a practical electrical resistance measurement is a cost-effective health and usage monitoring technique for carbon fiber reinforced composites.</p>