Epitaxial growth of La0.66Sr0.33MnO3 (LSMO) layers has been successfully achieved on SrTiO3(001) and MgO(001) substrates using RF magnetron sputtering with facing targets. The magnetic behavior of the films was analyzed before the structure was investigated by X-ray diffraction and transmission electron microscopy (TEM) performed on plan-view and cross-sectional specimens. We report the influence of the deposition conditions and nature of substrate on the growth and magnetic properties of the layers. The study of the relaxation mechanisms in the different specimens gives evidence for both epitaxial strain and rhombohedral distortion relaxation. Their occurrence strongly depends on the growth conditions, which in turn controls the oxygen stoichiometry in the samples and their magnetic properties, (C) 2002 Elsevier Science B.V. All rights reserved.