The diffusion of nickel into copper and copper–nickel alloys are investigated in the temperature range of 780 to 1037 °C by the resistometric method and the diffusion coefficients and activation energies are obtained. The nickel diffusion in copper is compared with the previous studies. For the diffusion of nickel into copper–1.08 at% nickel and copper–2.81 at% nickel alloys no such comparison can be made as there are no data available in this dilution range. The diffusion coefficients of the systems studied show a strong dependence on the alloy composition. It is also observed that addition of nickel into copper retards the diffusivity. The data obtained from the studies are analysed in the light of the theories of LeClaire and Neumann and Hirschwald.