Perovskite oxides of formula La1−xSrxMnO3 have been obtained by the thermal decomposition of precursor powders. Two different kinds of precursors, carbonates and citrates have been prepared by low temperature, i.e., “chimie douce” technique. The careful control of the chemical and the hydrodynamic parameters during the synthesis process allows obtaining nice homogeneous and small size particles (80 nm for the ex-carbonates and 30 nm for ex-citrates). Pure perovskite phase is observed after a low temperature thermal treatment, from 550 °C. The structure of these oxides is either rhombohedral or cubic and depends on the strontium content, the temperature and the partial pressure of oxygen during the thermal treatment. The Mn-O distances and the Mn-O-Mn angles are directly related to the amount of Mn4+ content.