3D NiO nanowalls are homogeneously grown on macroporous nickel foam by a hydrothermal method. The morphology of the NiO nanowalls are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the phase structure of NiO nanowalls is characterized by X-ray diffraction (XRD) analysis. The results indicate that the NiO nanowalls are uniformly distributed on the entire nickel foam framework. And ammonia fluoride has significant influence on the height and thickness of NiO nanowalls. With the presence of ammonia fluoride, NiO nanowalls with height of 4.6 (+/- 0.4) mu m and thickness around 50 nm were obtained, while the height and thickness decreased to 1.7 (+/- 0.2) mu m and around 20 nm without the presence of ammonia fluoride. The NiO nanowalls were used as electrodes for urea oxidation in alkaline condition. The electro-oxidation activity the catalyst is investigated by cyclic voltammetry and potential step chronoamperometry. The electrocatalytic performance of NiO electrodes depends strongly on the sample preparation condition. The 3D NiO nanowalls electrode exhibit excellent electro-oxidation activity towards urea oxidation. The morphology of the electrodes has significant influence on their activity. The current density of 3D NiO nanowalls electrode prepared with NH4F at 0.7 V reached 800 mA cm(-2), which was over 4 times than that of sample prepared without NH4F. Moreover, NiO nanowalls prepared with NH4F was more stable than the one prepared without NH4F, which did not show any appreciable morphology change after being used for urea electro-oxidation for 12 h. While the one prepared without NH4F collapsed after used.