In this work, the surface of nano/micro-E-glass fibril (nGF) was modified with an amine silane coupling agent before applying as toughener for epoxy resin. The chemical structure and composition of silanized glass fibril (s-nGF) were also confirmed and compared with virgin nano/micro-glass fibrils. The curing reaction of epoxy samples with various s-nGF contents was performed at room temperature. Many characteristics of composite samples were also examined such as mechanical properties, fracture energy, thermal stability, and morphology. The experimental testing indicated that the s-nGF helps to improve the mechanical, thermal stability as well as the fracture energy of epoxy resin. The morphology observation also indicated that the s-nGF prevented the crack growth inside the epoxy matrix as the main reason of the enhancing fracture energy of epoxy resin with the presence of s-nGF.