Au nanoparticles (NPs) embedded in silica matrix were synthesized by atom beam co-sputtering and investigated in detail by transmission electron microscopy (TEM). A study on electron beam induced tailoring of size of Au nanoparticles has been performed in an in-situ TEM experiment as a function of electron irradiation time. This study concludes that electron beam irradiation can result in a controlled growth of NPs in proportion to irradiation fluence. Analytical calculations for electron energy loss in Au NPs and fused silica have been performed, which indicate that the observed growth of Au NPs in present case is due to rise in temperature of Au NPs and surrounding silica.