Three Ni–P–O compound catalysts with tunable architectures and compositions have been fabricated using a facile one-pot solvothermal method, which are named astrocyte-network Ni–P (Ni–P_an), silkworm cocoon-like Ni–P (Ni–P_sc), and microsphere Ni–P (Ni–P_m), respectively. The final architecture of the Ni–P–O catalysts is strongly dependent on the Ni²⁺/H₂PO₂⁻ molar ratio in the reaction system, which leads to a delicate balance between kinetic and thermodynamic growth regimes. Three-dimensional ensemble of Ni–P_an with a higher P content is composed of many amorphous Ni–P nanowires with a diameter of about 4 nm, which delivers a significantly larger BET surface area of 500.5 m² g⁻¹. Moreover, nickel phosphides and nickel phosphates are formed in the three Ni–P–O samples. Ni–P_an exhibits a higher peak current density of ∼1490 A g⁻¹, better electrode accessibility, faster charge-transfer process, and long-term chronoamperometry stability (≥20 000 s) toward methanol oxidation in alkaline solution, which are superior to most state-of-art Ni–P catalysts and the Ni–P_sc and Ni–P_m in this case. The superior catalytic performance of the Ni–P_an catalyst is attributed to its unique microstructure and compositions. According to X-ray photoelectron spectroscopy, a strong electronic interaction between nickel phosphides and nickel phosphates might also contribute to the improved catalytic activity of the Ni–P_an catalyst.