Ultrathin silver films (4.0, 6.2, 12.5, 26.2, 30.0 and 40.6 nm) were prepared by direct current sputtering deposition. The thicknesses and optical constants of the films were studied by spectroscopic ellipsometry. The Drude model combined with Lorentz Oscillator model was used in the optimization of the ellipsometric data. The results show that surface plasma resonance absorption (SPR) peaks appear in the spectra of extinction coefficient k for samples 1, 2, 3 and 4. The peak shifts to shorter wavelength with the reduction in film thickness. The wavelengths of the SPR for different films were calculated by the SPR theory and also compared with the experimental data.