Bismuth ferrites crystallites were synthesized by a polyvinyl alcohol (PVA) modified hydrothermal method. X-ray diffraction (XRD) analysis indicated that the pure phase of Bi25FeO40, BiFeO3 and Bi2Fe4O9 were synthesized with initial Bi/Fe ratio of 1:1 at the temperature of 200°C for 24 h, using NaOH concentration of 2, 5 and 10 M, respectively. With addition of PVA, the individual Bi-Fe oxides could be existed in a more wide range of processing parameters. The phase evolution of bismuth ferrites in the process of hydrothermal reactions was discussed. Moreover, photocatalytic properties of the bismuth ferrites crystallites were explored. The results showed that they possessed band gaps of about 2.0 eV and performed good degradation effect at visible light region.