In this study, three La₂O₃ hierarchical micro/nanostructures, nanospindles, nanopolyhedra and nanospheres, were synthesized to remove phosphate from microbial growth media for bacterial inactivation as an antimicrobial strategy. The experiment results showed that the morphology of La₂O₃ hierarchical micro/nanostructures can be controlled by the concentration of the reactants, reaction temperature and cooling treatment. Meanwhile, the properties of the La₂O₃ were researched for phosphate removal and antibacterial activity. The results showed that the different morphologies of the La₂O₃ micro/nanostructures had different removal abilities for phosphate, and can differently inhibit growth of bacteria. Spherical La₂O₃ possesses the best removal ability and antibacterial activity, which indicates that the smaller the La₂O₃ hierarchical micro/nanoparticles are, the stronger the phosphate removal capacity. Compared with nanoparticles, the hierarchical micro/nanoparticles have a significant advantage: they not only have the properties of nanoparticles, but also are relatively stable, not easy to aggregate, and are easy to separate after the reaction. Therefore, the La₂O₃ hierarchical micro-nanomaterials may have very good application prospects for phosphate reduction in open water and to inhibit algae overgrowth.