Two dimensional (2D) square-like bismuth oxyiodine (BiOI) nanosheets with a thickness of about 10 nm and exposed {001} facets are obtained by a facile hydrothermal route without any surfactant and special solvent. The photocatalytic performance of as-prepared 2D square-like BiOI nanosheets is evaluated by the photodegradation of rhodamine-B (RhB), methyl orange (MO) and phenol under visible-light irradiation. The products show highly efficient photocatalytic performance and good photostability and recyclability under visible light irradiation. The efficient visible-light driven photocatalytic activity can be ascribed to the thin 2D square shape nanosheet with exposed {001} facets, which provides an appropriate diffusion length and self-induced internal static electric field direction of BiOI, and improves the separation efficiency of photoinduced electron-hole pairs in BiOI nanosheets. Furthermore, the thin nanosheets that have a greater percentage of {001} facet exposure could induce stronger internal static electric fields, and improve the photocatalytic activity.