Bi₂MoO₆/Bi₂O₃ heterojunction photocatalysts were synthesized through a facile alkali etching method and their photocatalytic activity was evaluated by photodegradation of Rhodamine B (RhB) under visible-light irradiation. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectroscopy. XRD, TEM and XPS results confirm that the Bi₂MoO₆/Bi₂O₃ heterojunctions were formed after the alkali etching process. The photocatalytic activity can be easily controlled by adjusting the etching time and the highest visible-light-responsive photocatalytic performance was observed on Bi₂MoO₆/Bi₂O₃ composite that was etched in 0.1 M NaOH for 45 min. Moreover, the mechanistic study suggested that the photoinduced holes played a major role for the RhB degradation and the photocurrent tests confirmed that the effective electron–hole separation on the interface of the p–n junction promotes the photocatalytic process.