The peculiarities of optical adsorption and percolation in thin Ag films of different thicknesses (2–20 nm) and influence of 0.5 nm thickness Si underlayers on it in visible and near-infrared wavelength regions (300–2500 nm) is investigated experimentally. The peculiarities of growth mechanism and the mode of metal film formation on an amorphous glass substrate have main impact on percolation phenomena in silver thin films. The 0.5 nm Si underlayers decrease the threshold thickness dc of percolation in Ag films on $\Delta d$=5.5 nm, which exhibits in the optical properties. Such samples have higher optical adsorption versus Ag films deposited on pure glass substrate, because of the finer polycrystalline structure of Ag films on Si and higher concentration of isolated metal islands on substrate.