A family of bismuth ferrites (BFO), including Bi2Fe4O9, BiFeO3, and Bi25FeO39 with different morphologies, has been prepared by the hydrothermal method assisted by different alkaline mineralizers. X-ray diffraction refinement calculations are carried out to study the crystal structures of bismuth ferrites. A thermodynamic calculation based on the dissolution-precipitation model was carried out to analyze the hydrothermal synthesis of BFO powders. Magnetic measurements of the obtained bismuth ferrites show different magnetic properties from 5 K to 350 K.