The present paper shows the potential of fumed silica as nano-reinforcements in polymers, by considering the limitations and challenges one has to face dealing with nanoparticles in general. The dominating effect of the manufacturing route and surface properties of fumed silica influencing the resulting degree of dispersion and the interfacial adhesion were investigated by electron microscopy (TEM, SEM). The resulting (fracture-) mechanical properties of the fumed silica/epoxy composites were investigated for volume contents of 0.5 vol% and below. Independent of the surface modification, static and dynamic modulus decreased slightly by adding the fumed silica. Hence, the fracture toughness K-Ic turned out to be significantly increased (54%) adding only 0.5 vol% of surface modified fumed silica.