The surface plasmon resonance (SPR) phenomenon in the Kretschmann configuration comprising an SF10 glass prism, a gold coated SF10 slide and an analyte is analyzed theoretically and experimentally in the spectral domain utilizing the ratio of the re ectances of p- and s-polarized waves. Using the dispersion characteristics of a metallic layer according to the known model, the analysis for one angle of incidence can give the results that agree well with the experimental data. However, if the different angles of incidence are considered, the agreement fails because the SPR response is very sensitive to the dispersion characteristics of a metallic layer. A simple technique to obtain the dispersion of the complex permittivity of a metallic layer is proposed. To minimize the effect of an analyte, the SPR phenomenon is considered for air when a desirable angle of incidence is adjusted. Using this technique, we measure parameters of the ratio of the reflectance's of p- and s-polarized waves at different angles of incidence, that is, the minimum of the reflectance ratio and the resonance wavelength, to obtain the real and imaginary part of the complex permittivity. In the processing of every dip, we used the linear approximation of the real part and the quadratic approximation of the imaginary part of the complex permittivity of gold. The dispersion of the gold layer thus retrieved is compared with the model dispersion.