Abstract: This paper has investigated the effect of substrate temperature on the residual stress and microstructure of Ag-MgF₂ cermet films prepared by vapor deposition. X-ray diffraction (XRD) technique was employed to study the microstructure of the films. The results show that the average stress over a φ20.4 mm round area is the least and the residual stress of the films appears to be tensile stress between 300℃ and 400℃. Crystal lattice constants of Ag and MgF₂ both approach the bulk values. The residual stress of the films can be decreased by altering the substrate temperature.