The synthesis and shape evolution of alpha-Fe2O3 nanoparticles through oriented aggregation in solvothermal system were investigated. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) revealed that the three-dimensional (3D) flower-like alpha-Fe-2-O-3 nanophase was formed by two-step crystallographically oriented aggregations, and then evolved to polyhedral nanoparticles by conventional Ostwald ripening. The organic solvent N, N-dimethylformamide (DMF) played an important role not only in chemical reaction, but also in oriented aggregation-based self-assembly. (c) 2005 Elsevier B.V. All rights reserved.