Two-dimensional Ni(OH)₂ is a cheap and promising urea oxidation reaction (UOR) catalyst, but its catalytic performance is seriously hampered by fatal disadvantages including sluggish kinetics, limited exposed active sites in the bulk and unsatisfactory stability. Herein, we report a chlorine-anion modified nickel hydroxide nanosheet (Cl–Ni(OH)₂) with much better charge transfer, more active centers and improved working stability using an easy-operation method at room temperature. Impressively, the optimal Cl₃₂–Ni(OH)₂ catalyst delivers a current density of 106.93 mA cm⁻² at 1.6 V vs. RHE and a Tafel slope of 42.37 mV dec⁻¹, much better than those of pristine Ni(OH)₂ (20.38 mA cm⁻², 100.40 mV dec⁻¹). Moreover, Cl₃₂–Ni(OH)₂ exhibits excellent long-term durability over 15 h under 10 mA cm⁻². This work provides an efficient catalyst for the UOR and affords a simple method to improve the electrocatalytic activity of two-dimensional catalysts for energy conversion.