Different bismuth subcarbonate ((BiO)(2)CO3) hierarchical nanostructures assembled by nanoplates or nanosheets have been successfully synthesized via a simple hydrothermal route by properly monitoring experimental conditions. The; synergistic effect of citrate ions, urea, and solvent is of crucial importance for the controllable fabrication of (BiO)(2)CO3 hierarchical nanostructures. The citrate ions play a key role in the assembly of 3D hierarchical nanostructures. The amount of, urea could mediate the thickness of 2D structural units. The solvent could not only influence the thickness of the 2D structural unit but also mediate the structure and assembly of hierarchical nanostructures. On the basis of experimental observation, a possible formation process (BiO)(2)CO3 hierarchical,nanostructures was preliminarily proposed. The photocatalytic performance of the as prepared (BiO)(2)CO3 hierarchical nanostructures was evaluated by the photodegradation of Rhodamine B (RhB) upon UV light irradiation. It indicated that loose packed flower-like (BiO)(2)CO3 hierarchical nanostructures assembled by ultrathin nanosheets with large BET surface area and narrow band gap displayed the best photocatalytic activity and favorable recycling characteristics.