The research is aimed to investigate the influence of spherical nanoparticles on the fracture behavior of glass fiber/epoxy composites. Two different contents of silica nanoparticles, 10wt% and 20wt %, were introduced into the composite samples. Through a sol-gel technique, the silica particles with diameter of 25 nm were dispersed uniformly into the epoxy matrix. Subsequently, the silica epoxy mixtures were impregnated into the unidirectional glass fiber mat by means of a vacuum hand lay-up process to form the unidirectional glass fiber/epoxy laminate. During the fabrication, a porous film was inserted into the mid-plane of the laminate to generate the pre-crack. The Mode I fracture toughness of the composites with different nanoparticles contents were then determined form the double cantilever beam (DCB) specimens. Based on the experimental observations, it was found that the glass fiber/epoxy composites with silica nanoparticles exhibit superior fracture toughness than those that do not contain any silica particles. Scan Electronic Microscopy (SEM) observations on the failure surfaces indicated that the enhanced fracture toughness could be due to the improved interfacial bounding in conjunction with the nanoparticle debonding from the surrounding epoxy. In general, such failure mechanisms may complicate the fracture process, dissipating more fracture energy.