Crystal structure and microstructure of La0.7-xLuxSr0.3MnO3 (x = 0.2 0.45, 0.6) prepared by usual ceramic techniques and grinding procedure are studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). With substitution of Lu3+ for La3+ and Sr2+, LSMO rhombohedral phase has been gradually converted to the stable hexagonal phase LuMnO3. Surprisingly, XRD and the energy-dispersive X-ray spectroscopy (EDS) analyses have demonstrated that both lattice parameters (a- and c-lengths) and the La3+/Sr2+ atomic ratio of the rhombohedral phase are decreasing with increasing x. The abnormal phenomenon is related to the fact that the Mn3+/Mn4+ atomic ratio in the reactant is changed accompanying with combination of Lu3+ and Mn2O3. (c) 2005 Elsevier B.V. All rights reserved.