Nickel oxide was prepared by anodic deposition in a basic solution comprising nickel chloride, ammonium chloride and ammonia. The influence of ammonia was investigated using galvanostatic reduction techniques and cyclic voltammetry (CV). It was found that the oxidization peak potentials shift positively with decreasing ammonia concentration, while the oxidization peak currents firstly increase with decreasing ammonia concentration and then decrease when the ammonia concentration is lower than 1.67 mol L-1. This is mainly attributed to the fact that the equilibrium concentration of Ni(OH)(2(aq)) varies with the ammonia concentration. A potential plateau at about 0.75 V was observed in galvanostatic reduction curves for nickel oxide, and the length of the potential plateau in solution with 1.67 mol L-1 ammonia concentration was longer than that in the other solutions, which agreed well with the CV results.