Residual stresses in ultrathin La0.9Sr0.1MnO3 (LSMO) films with various thicknesses of 8-40 nm were measured quantitatively via synchrotron radiation X-ray diffraction. By fitting the strain versus sin(2)psi plots the residual stresses in the nanofilms were obtained. With increasing film thickness, both the in- and out-of-plane stresses decreased for strain relaxation. The strains of LSMO nanofilms on miscut SrTiO3 (STO) substrates were weaker than those on exact-cut ones with same thickness, which indicates that the crystallization in nanofilms on miscut SrTiO3 was more perfect than that on exact-cut SrTiO3. The mechanism is discussed briefly based on the minimization of surface energy and strain energy. (C) 2012 Elsevier B.V. All rights reserved.