In this study, the interlaminar region of a carbon fiber composites was reinforced with silica nano-particles, and its effect on the in-plane mechanical response was investigated. Also, the effect of particles on the dynamic interlaminar shear strength of composites was studied. Two batches of composite specimens, one batch made of only fiber and matrix and the other with nano-silica added as a third phase, were fabricated. The composite specimens were prepared through a high-temperature molding process, where the nanoparticles were dispersed on the surface of the prepreg layers before stacking. For in-plane properties, standard tensile test coupons were made with fibers oriented at a different angle relative to the loading direction. For interlaminar shear properties, a V-notch bending and three-point bending specimens were prepared. It was found that the nanoparticles have a sound influence on the in-plane mechanical response mainly on the in-plane shear property of the composite. On the other hand, the nano-filler has shown a significant effect on the dynamic interlaminar shear strength of the laminate.