Bi2Fe4O9 crystals were successfully prepared via a rapid and facile microwave hydrothermal (MH) process. The influences of the various preparation parameters (including the NaOH concentration, and holding time) on the phase formation and morphology development were investigated in detail. XRD results showed that Bi2Fe4O9 crystal was formed indirectly with an intermediate phase of Bi25FeO40 in the MH process, whose further formation mechanism was discussed based on the morphology development. Moreover, the photocatalytic efficiencies of Bi2Fe4O9 products obtained at the different holding times were evaluated by the degradation of methyl orange under visible light irradiation. It was found that the photocatalytic activities were greatly dependent on the holding time. (C) 2012 Elsevier B.V. All rights reserved.