Visible-light-induced photocatalysts Bi 2 MO 6 (M=W, Mo) nanocrystals have been successfully synthesized via a new ultrasonic-assisted method. Laminar structured Bi 2 WO 6 nanoplates with size of ca. 100nm and Bi 2 MoO 6 nanoparticles with size of ca. 150nm were prepared via ultrasonic pretreatment followed by calcination at 500°C. The photocatalytic activities of as-prepared Bi 2 MO 6 were about 4–6 times higher than that of the products prepared by traditional solid-state reaction (SSR), which were evaluated by the degradation of RhB dye in water under visible light irradiation (λ>400nm). It was found that ultrasonic irradiation played an important role in the formation of the nanomaterials with a smaller crystal size and larger surface area, which was beneficial to their photocatalytic activities. The present study suggested a promising method, as an effective improvement of traditional SSR-process, for the synthesis of other photocatalysts.