Effect of tetraborate ions on Ni-Cu alloy electrodeposited from a pyrophosphate bath has been studied. Deposits from a tetraborate-free bath were non-uniform, blackish and contaminated with insoluble compounds, which was confirmed to be nickel hydroxide hydrate by X-ray diffraction and X-ray photoelectron spectroscopic analysis. In contrast, the deposits from a bath containing sodium tetraborate were smooth, fine-grained, nickel-rich and gave nickel-like lustrous appearance. Sodium tetraborate was found to improve the quality of Ni-Cu alloy deposits by preventing the increase of pH at electrode/electrolyte interface and the precipitation of the insoluble nickel hydroxides.