In this paper, optical and structural properties of ZnS and MgF2 multilayers grown by thermal evaporation are studied. Effects of annealing at different temperatures on samples with different number of layers are investigated. The maximum of reflection is shifted to different wavelengths, depending on the number of layers of the annealed samples. Using X-ray diffraction analysis, structural properties have been studied, and grain size and microstrain have been obtained by the Scherrer-Wilson formula, with grain sizes ranging from 10 nm to 22 nm for MgF2 and from 0.9 nm to 210 nm for ZnS, and microstrain values from 2.5 x 10(-3) to 3 x 10(-3) for MgF2, and from 1.2 x 10(-3) to 2.6 x 10(-3) for ZnS. Competition between crystallite size and microstrain is observed. (C) 2010 Elsevier B.V. All rights reserved.