Recently, highly active, easy-to-make, and efficient bifunctional electrocatalysts have attracted tremendous attention because of their potential applications in clean energy. Herein, we report a simple, one-step approach for fabricating three-dimensional (3D) Ni–P nanorod arrays by direct phosphorization of commercial nickel foam (Ni foam) with different times. When used as a 3D electrode for oxygen evolution reaction, the obtained Ni–P nanorods with two hours of phosphatization treatment display high activity with an overpotential of 270 mV required to generate a current density of 30 mA/cm2 and excellent stability in 1.0 M KOH. Additionally, the Ni–P nanorod arrays are also highly active for electrocatalyzing the hydrogen evolution reaction in the alkaline media. As a result, the bifunctional Ni–P catalysts enabled a highly performed overall water splitting, in which a low applied external potential of 1.6 V led to a stabilized catalytic current density of 10 mA/cm2 over 12 h.