In this work, large-sized Bi4Ti3O12 square nanosheets with highly exposed (010) facet were synthesized by a hydrothermal route. It is demonstrated that the lateral size of Bi4Ti3O12 square nanosheets reaches as large as 14 mu m, while their average thickness is only about 60 nm, implying that the nanosheets have nearly 100% exposed (010) facet. The photocatalytic activity of Bi4Ti3O12 nanosheets was evaluated by RhB under simulated sunlight irradiation, revealing that they exhibit an excellent photocatalytic activity. The highly photocatalytic activity of the (010) facet can be ascribed to the fact that photogenerated electrons and holes are readily separated along the (010] direction and migrate to the (010) facet under the action of the polarization electric field, and moreover, the electronic structure calculations revel that the surface energy of the (010) facet is much larger than those of other facets like (100) and (101) facets.