Nanoscale lanthanum manganites (LaMnO 3+δ ) were prepared with thermal decomposition of precursors derived from hydrothermal synthetic method. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed that the as-prepared sample is composed of nanofilaments in an amorphous form. The as-prepared nanoparticles were hydrothermally treated at 180 °C for 12 h and then were annealed at 600, 800, and 900 °C for 4 h to form LaMnO 3+δ . With increasing annealing temperature, a shape change from filaments to rods to spheres was found, and their diameters increased from 4.5 to 52.9 nm. XRD showed a chemical transformation from La(OH) 3 to LaMnO 3+δ . Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are used to investigate the change of the of local atomic structure around La/Mn with increasing annealing temperature. Combining the TEM, XRD, XANES and EXAFS results, the La-compound is found to be embedded in an amorphous Mn compound with medium range order. As annealed at different temperature, the chemical transformation process from La(OH) 3 to LaMnO 3+δ was discussed. It was the chemical transformation that drives the shape change of these nanomaterials.