The quality of coat applied from sulphate electrolyte of Ni plating at pH 4.6-5.6 and 50° C was studied as a function impurities contained. It is shown that to have void-free Ni deposits the NiSO4 concentration in the electrolyte must be maintained within 250-280 g/l at pH 5.4-5.6 and electrolyte must be thoroughly cleaned from iron impurities. Fe ion impurities available in electrolyte sharply degrade the quality of Ni plating parts of water electrolyzer. Rigid control of changes in Fe ion concentration of electrolyte is recommended, clean-up and filtration of solution must be continuous. Maximum permissible Fe concentrations in sulphate electrolytes of Ni plating must not exceed 0.01g/l, in sulphamate electrolytes they are much lower.