Bismuth ferrite crystallites were prepared by the hydrothermal method. The phase evolution in the process of hydrothermal reactions was investigated for different conditions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicates that sillenite Bi25FeO40 could be the intermediate products, while perovskite BiFeO3 was the target crystallite. The phase evolution could be controlled by adjusting KOH concentration, reaction temperature and duration time et al. The dissolution of Fe(OH)(3) plays an important role to control the phase formation of bismuth ferrites. Bi25FeO40 and BiFeO3 crystallites have the cubic and sphere-like morphologies respectively. The formation of perovskite BiFeO3 crystallites was based on the dissolution of sillenite Bi25FeO40. (C) 2012 Elsevier B.V. All rights reserved.