Two-dimensional (2D) nanomaterials are extraordinarily attractive for use in energy storage devices because of their unique electronic and mechanical properties. However, the synthesis of ultrathin 2D nanomaterials is still a great challenge. In this paper, a top-down strategy using a high-pressure hydrogen surface treatment and controlled etching to reduce the thickness of iron(III) oxide (Fe2O3) nanoplates is proposed. As a result, the ultrathin Fe2O3 hexagonal nanoflakes with a thickness of approximately 4 nm are successfully synthesized. When employed as an anode material in rechargeable lithium-ion batteries, it delivers a super-high reversible capacity of approximately 1043 mA h g−1 after 100 cycles at a current density of 0.1 A g−1 and approximately 578 mA h g−1 after 500 cycles at a current density of 5.0 A g−1. It is also the best performing Fe2O3 electrode among the reported Fe2O3 anodes in the literature. Such excellent cycling performances can be attributed to the ultrathin structure which is able to enhance the mass transport of the lithium ion, short electron transport length as well as tolerance of large volume changes. This work provides a guidance to the synthesis of ultra-thin 2D oxide nanomaterials for energy storage.