In this work, we investigate ZnS:Mn polycrystalline thin films deposited onto glass substrates coated by tin or bismuth buffer layers, by using X-ray diffraction in the conventional Bragg-Brentano geometry. The ZnS:Mn thin films were deposited via radio frequency magnetron sputtering from a ZnS:Mn target (0.1% atomic Mn) and the buffer layers by thermal vacuum evaporation. A suitable algorithm were introduced in the Rietveld routine for powder diffraction data in order to model the X-ray diffraction patterns of the multilayers. The experimental results reveal that the microstructure and the crystalline phase of the ZnS films depend decisively on the structural and microstructural properties of the buffer layers.