High dose Ag+ implanted SiO2 glass and subsequently annealing were investigated by Rutherford baekscattering and optical absorption techniques, optical absorption spectra showed that the implanted Ag+ coalesce into colloidal particles, the plasma resonance maximum is at 400 nm. The Ag colloid of 18 A in radius was estimated from measurements of the half-width of the plasma resonance by using the Mie theory and Doyle method.