Several times, preferred properties are not accomplished when the fiber-reinforced composites are tested after they are prepared and the similar observations are also observed in the case of nanoparticle-reinforced composites. While the composites are manufactured under controlled conditions with stringent quality measures, it is complex to circumvent fiber-matrix interfacial debonding. The amount of debonding decides the final mechanical properties of composite material. In this study, an effort is made to quantify the debonding effect of nanoparticles on mechanical properties of nanoparticle-filled composites using finite element models with homogenization approach. Buckminster fullerene and conventional fiber T300 are selected as reinforcement medium. The predictions revealed that the longitudinal Young's modulus is not affected by debonding.