Highly active, durable, and inexpensive nanostructured catalysts are crucial for achieving efficient and economical electrochemical water splitting. However, developing efficient approaches to further improve the catalytic ability of the well-defined nanostructured catalysts is still a big challenge. Herein, we report a facile and universal cation-exchange process for synthesizing Fe-doped Ni(OH)2 and Co(OH)2 nanosheets with enriched active sites toward enhanced oxygen evolution reaction (OER). In comparison with typical NiFe layered double hydroxide (LDH) nanosteets prepared by the conventional one-pot method, Fe-doped Ni(OH)2 nanosheets evolving from Ni(OH)2 via an Fe3+/Ni2+ cation-exchange process possess nanoporous surfaces with abundant defects. Accordingly, Fe-doped Ni(OH)2 nanosheets exhibit higher electrochemical active surface area (ECSA) and improved surface wettability in comparison to NiFe LDH nanosheets and deliver significantly enhanced catalytic activity over NiFe LDH. Specifically, a low overpotential of only 245 mV is required to reach a current density of 10 mA cm-2 for Ni0.83Fe0.17(OH)2 nanosheets with a low Tafel slope of 61 mV dec-1, which is greatly decreased in comparison with those of NiFe LDH (310 mV and 78 mV dec-1). Additionally, this cation-exchange process is successfully extended to prepare Fe-doped Co(OH)2 nanosheets with improved catalytic activity for oxygen evolution. The results suggest that this cation-exchange process should have great potential in the rational design of defect-enriched catalysts toward high-performance electrocatalysis.