Identifying the influence of the phase of a catalyst on its reactivity is crucial for guiding the rational design of highly active electrocatalysts. Herein, we unveil the phase-dependent reactivity of nickel molybdates (NiMoO₄) for the electrocatalytic urea oxidation reaction (UOR). Various NiMoO₄ phases, namely, α-NiMoO₄, β-NiMoO₄, and the hydrate NiMoO₄·xH₂O, were synthesized, and their structural characteristics and electrochemical properties were related to their electrocatalytic performance for the UOR. The NiMoO₄ phase was found to determine its reactivity, and phase-dependent UOR activities were observed. In particular, β-NiMoO₄ exhibited a higher activity and faster kinetics than NiMoO₄·xH₂O and α-NiMoO₄, which was attributed to the large electrochemical surface area, low Tafel slope, and small charge–transfer resistance of β-NiMoO₄. Moreover, hydrogen generation via β-NiMoO₄-catalyzed urea electrolysis achieved a much lower cell voltage (1.498 V to reach 10 mA cm^–2) than that required for water electrolysis (1.633 V to reach 10 mA cm^–2). This work provides insights into design strategies for high-activity electrocatalysts for energy-efficient hydrogen production.