X-ray photoelectron spectroscopy (XPS) has been used to investigate grain boundary diffusion of Ag through 250 Å thick Ni80Fe20 (permalloy) films in the temperature range of 375 to 475°C. Grain boundary diffusivities were determined by modeling the accumulation of Ag on Ni80Fe20 surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Ag through Ni80Fe20 is characterized by a diffusion coefficient prefactor, D0,gb, of 0.9 cm2/sec and an activation energy, Ea,gb, of 2.2 eV. The Ni80Fe20 film microstructure has been investigated before and after annealing by atomic force microscopy and x-ray diffraction. The microstructure of Ni80Fe20 deposited on Ag underlayers remained relatively unchanged upon annealing.