This study is focused to see reinforcing effects of SiO2 nanoparticles on the mechanical and thermal properties of epoxy resin. For the same, SiO2 nanoparticles up to 8 wt.% were reinforced in epoxy resin and the effect of this reinforcement was seen on fracture toughness, fracture energy and glass transition temperature. The particles were dispersed ultrasonically in epoxy resin, which gives well dispersion of nano-SiO2 particles. A good dispersion of silica nanoparticles enhances mechanical and thermal properties up to 4 wt.% SiO2. As a result, the value of fracture toughness increases from 1.10 to 2.90 M Pa.m1/2, fracture energy increases from 2.66 to 11.50 kJ/m2 and glass transition temperature increased about 9°C for the epoxy containing 4 wt.% SiO2 nanoparticles. With further particle loading in epoxy reflected decrease in mechanical and thermal properties, which is attributed to the significant increase in clustering of the nanoparticles at higher loading concentrations.