Silver films containing a small amount of SiO2 were prepared by an r.f. sputtering technique. The volume ratio of SiO2 to the total volume of the film, f, was estimated from the density measurements. Attenuated total reflection (ATR) spectra were measured for the composite films having various values of f ranging from 0 to 10%. Although the transmission spectra of the films did not change appreciably in this range of f : the ATR spectrum was found to change drastically depending on f. A comparison of theoretical ATR spectra with experimental ones suggests that the observed changes in the ATR spectrum can qualitatively be explained by the changes in the effective dielectric constant of the composite film due to the inclusion of a small amount of SiO2 into Ag films.