Silver negative ion implantation into 50- and 25-nm-thick SiO2 film on Si and subsequent heat treatment were conducted to form nanoparticles. Optical properties showed formation of Ag nanoparticles in the films. Transmission electron microscope (TEM) images of the 50-nm-thick SiO2 sample implanted at 30 keV showed nanoparticles with diameter of several nm. The location of nanoparticles corresponded to the calculated profile. On the other hand, the 25-nm-thick SiO2 sample implanted at 10 keV with dose of 5×1015 ions/cm2 showed monolayered crystallized nanoparticles along the interface of SiO2/Si. The Rutherford backscattering spectrometry (RBS) spectra showed Ag atoms distributed at the surface and at a depth corresponded to the calculated profile after annealing at 500 °C. The surface accumulation seems to be resulted from thermal diffusion of implanted atoms during implantation. A small peak in concentration was also observed at 22 nm in depth. This suggests existence of a diffusion barrier for Ag atoms. At 700 °C, a main peak appeared at 20 nm in depth.