The present study utilized piezoresistive carbon nanotube (CNT) fibers for the structural health monitoring of composites. In particular, diversified schemes including i) Pre-casted CNT fiber patches embedded into GFRP composites, ii) CNT fibers stitched to one glass fabric of the composites during the fabrication procedure, and iii) CNT fibers attached to the top of the composites, were proposed for incorporation of CNT fibers to the composites. The fabricated samples were subjected to cyclic tensile loadings with constant and increasing amplitudes to assess their piezoresistive characteristics. All types of samples showed sharp increases and decreases in the electrical resistance values, reflecting the applied stress. They also showed good sensing integrity under extended cyclic loadings as well as against loading up to the point of failure. Moreover, the fabricated composites exhibited tensile strengths comparable to those of the control samples, demonstrating feasibility to be used as a sensor of composite structures.