Powders of perovskite LaMnO3+delta with large over-stoichiometry coefficient delta up to delta = 0.29 have been synthetized by two different soft chemistry routes using hydrothermal treatment at 150 degreesC and sol-gel process. Structural and morphological properties were examined by thermal analysis, X-ray diffraction and transmission electron microscopy. Rietveld refinement led to rhombohedral distorted perovskite for all the over-stoichiometric LaMnO3+delta with 0.10 < delta < 0.29. These studies confirm from structural parameters analysis the solubility limit of cationic vacancies previously evidenced by Maurin et al. by X-ray absorption spectroscopy. Special attention was devoted to the correlation between grain size, synthesis pathways, calcination temperature and the formal Mn-IV content. (C) 2003 Elsevier Ltd. All rights reserved.