Metal phosphides (MPs) synthesized by solid-state reaction have shown considerable potential in hydrogen evolution reaction (HER) from water splitting compared with that of Pt. However, large-sized MP nanoparticles (NPs) with irregular morphologies are inevitably achieved via the solid-state reaction with high-temperature calcination, which lead to the reduced availability of the active sites. Here, a simple and straightforward strategy was developed to synthesize monodispersed, uniformly distributed, and small RhxP NPs decorated on phosphorus-doped nitride carbon (PNC) via the pyrolysis of rhodium(III) chloride, triphenylphosphine, and melamine (RhxP/PNC-m). The RhxP/PNC-m that served as a HER electrocatalyst displayed excellent performance with the overpotentials of 24 and 27 mV at 10 mA cm(-2) in basic and acidic solutions, respectively. This catalyst also showed good long-term stability in both media. The high-performance of RhxP/PNC-m should be attributed to the small, monodispersed, and highly distributed RhxP NPs on PNC support, which can supply abundant catalytically active sites for HER. The developed strategy for the synthesis of small RhxP NPs may offer new opportunities toward the electrochemical applications of other metal phosphides.