This study focuses on the optimizing the microstructure to improve the efficiency for healing interfacial debonding in fiber-reinforced polymers (FRPs). Healing is accomplished by incorporating a microcapsulated healing agent and catalytic chemical trigger within a coating layer on the surface of the fiber strands. Self-healing is demonstrated on flat tensile specimens of unidirectional FRPs. The effects of microcapsule diameter and concentration, and number of filaments in the fiber strand on tensile strength of virgin and healed specimens are discussed. Microstructure of the fracture surfaces of specimens was also examined by a scanning electron microscope. Additionally, finite element analyses were performed to predict the microcapsule-matrix debonding process during uniaxial tensile loading.