Silica nanoparticles were prepared from TEOS by the bench-scale aerosol reactor using the flame reaction. Silica nanoparticles having different average particle diameters were applied to measure the physical properties of Epoxy Molding Compound. Silica nanoparticles ranged from 10 to 40 nm were synthesized by changing the TEOS concentration in the diffusion flame. Spiral flow and bleed/flash of EMC were chosen as important physical properties which depend on the average particle size of silica nanoparticles. the results showed that silica particles less than 20 nanometer from the present study were very compatible with the commercial silica nanoparticles from SiCl₄ for the preparation of the EMC.