The electrochemical reduction of hydrogen peroxide on the copper-nickel alloys Cu90Ni10 and Cu70Ni30 in 0.1 M borax has been investigated. The results have been analysed on the basis of a chemical-electrochemical mechanism involving a surface Cu(I)/Cu(II) redox couple. The electrochemical step corresponds to the reduction of Cu(II) followed by the chemical reaction of Cu(I) with hydrogen peroxide. The rate of hydrogen peroxide reduction is strongly dependent on the rate constant of the chemical step. The potential dependence of the surface coverage by Cu(I) species accounts for the large values of the Tafel slopes. The catalytic effect of Cu(I) is similar to that of AuOH noted previously fbr the reduction of H2O2 on gold. Ellipsometric measurements also indicate the presence of an oxide/hydroxide layer at the interface at potentials very negative with respect to bulk Cu2O reduction.