Rational design of efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) has attracted wide attention. Noble metal-based electrocatalysts with ultrathin structures and highly exposed active surfaces are essential to boost the HER performance, while the simple synthetic strategies remain challenging. Herein, we reported a facile urea-mediated method to synthesize hierarchical ultrathin Rh nanosheets (Rh NSs) without using toxic reducing agents and structure directing agents in the reaction. The hierarchical ultrathin nanosheet structure and grain boundary atoms endow Rh NSs with excellent HER activities, which only requires a lower overpotential of 39 mV in 0.5 M H 2 SO 4 compared to the 80 mV of Rh nanoparticles (Rh NPs). Extending the synthesis method to alloys, hierarchical ultrathin RhNi nanosheets (RhNi NSs) can be also obtained. Benefiting from the optimization of electronic structure and abundant active surfaces, RhNi NSs only require an overpotential of 27 mV. This work provides a simple and promising method to construct ultrathin nanosheet electrocatalysts for highly active electrocatalytic performance. Hierarchical ultrathin Rh-based nanosheets exhibit excellent HER activities due to the advantages of structure, prepared with urea as directing agent.