The nickel-copper nanoalloys with tunable composition and morphology were prepared by galvanostatic deposition on copper substrate, in order to investigate the relationship between alloy composition and electrocatalytic activity. Both the composition and morphology of the NixCuy nanoalloys are highly dependent on the applied current density. The atomic ratio of Ni to Cu in the alloys changes from 1:9 to 3:1, with the increase of current density from 10 to 100 mA cm(-2). The difference in electrocatalytic activity among these nanoalloys was evaluated through the hydrogen evolution reaction (HER) in 1.0 M H2SO4 and 1.0 M KOH. The composition dependence of the electrocatalytic activity of the alloys is more pronounced in 1.0 M H2SO4 than in 1.0 M KOH. By tuning the composition of NixCuy alloys, 13.5 and 5.7 times increase in exchange current density of the HER was achieved in 1.0 M H2SO4 and 1.0 M KOH, respectively. Meanwhile, 4.5 and 2.0 times decrease in charge transfer resistance was observed in the same two media. The best electrocatalytic activity to the HER was always achieved on the nanoalloy with a 1:1 atom ratio and a single crystal (111) plane. This favorable nanoalloy is composed of four-level dendritic nanochains. The results demonstrate that galvanostatic method can tune not only the composition but also the morphology of nanoalloys, both being important for nanoscale design of industrial electrocatalysts.