Here we report for the first time of synthesizing ultrathin hematite nanoflakes (NFs) through an electrochemically induced morphological transformation from hematite nanorods (NRs). The NR–NF structural transformation was induced electrochemically at a negative potential (−1.2V vs. Ag/AgCl). The synthesized NFs have an average thickness of 10nm and an average diameter of 100nm. In comparison to NR, NF exhibits enhanced surface area and reduced charge transfer resistance, which are highly desirable for electrode materials of electrochemical devices. In this work, we investigated the mechanism of structural transformation and tested the performance of NR and NF electrodes for electrochemical capacitors and photoelectrochemical cells. Significantly, the NF electrode achieved an order of magnitude larger capacitance than NR electrode. The NF electrode also exhibited approximately three times higher photocurrent than NR electrode. This work opens up a new strategy to fabricate hematite electrodes with enhanced performance for electrochemical capacitors and photoelectrochemical cells, and can be potentially extended to other applications such as fuel cells and lithium-ion batteries.