The diffusion in Au-Cu and Pt-Cu thin films has been studied by Rutherford backscattering spectrometry (RBS) under the kinetic regime “B” (within the temperature interval of 175–290°C) and “C” (room temperature). The 1,5-2,0 MeV He+ RBS spectra were taken using 14–18 keV resolution. The RBS spectra were changed to depth-concentration profiles for both bulk and grain boundary (GB) diffusion. Under the kinetic regime “C” the absolute values of GB diffusion coefficients were obtained. Under the kinetic regime “B” the triple products δKDb, (δ is the GB width, Db is the GB diffusion coefficient, K is the enrichment ratio) were obtained using Whipple’s and Gilmer-Farrell’s models. The activation energies for both GB diffusion and bulk diffusion were determined for Au-Cu system as well as for Pt-Cu system. The comparison between the data on the GB diffusion for kinetics “B” extrapolated to room temperature and the data on the GB diffusion for the kinetics “C” enables one to derive the product δK and to separate the contribution of segregation into the parameters of GB diffusion for systems under study.