A novel flower-like Bi₂WO₆ superstructure was successfully realized by a facile hydrothermal process without any surfactant or template. Based on the evolution of this morphology as a function of hydrothermal time, the formation mechanism was proposed to be as follows: (1) self-aggregation of nanoparticles; (2) formation of crystalline nanoplates by Ostwald ripening; and (3) organization of the in situ-formed nanoplates into spherical superstructures. The pretty flower-like superstructure of Bi₂WO₆ was retained after calcination at 550 °C for 4 h. Both the uncalcined and calcined Bi₂WO₆ exhibited excellent visible-light-driven photocatalytic efficiencies for the degradation of Rhodamine B (RhB), up to 84 and 97% within 60 minutes, respectively, which were much higher than those of TiO₂ (P-25) and Bi₂WO₆ sample prepared by solid-state reaction (SSR-Bi₂WO₆). Close investigation indicated that plenty of pores with different sizes existed in the Bi₂WO₆ superstructures, which could serve as hierarchical transport paths for small molecules and might greatly improve their photocatalytic activities.