The influence of nickel addition to tin substrate on microstructure, kinetics parameters as well as diffusion coefficients was studied on Cu/Sn diffusion couples. The results revealed that the presence of nickel did not affect the growth of Cu3Sn phase in comparison with that of the binary Cu/Sn diffusion couple. However, it substantially influenced the morphology and chemical composition of the (Cu1-xNix)(6)Sn-5 phase, which grew with dual morphology and different chemical composition. The layer of the phase was poorer in nickel, whereas detached grains were richer in nickel concentration. The calculated kinetic parameters showed that the growth of the Cu3Sn and Ni-poor (Cu1-xNix)(6)Sn-5 phases was controlled by volume diffusion, but in the case of Ni-rich (Cu1-xNix)(6)Sn-5 phase, the growth was controlled by a complex mechanism. The calculations of diffusion coefficients and activation energies of Cu3Sn and Ni-poor (Cu1-xNix)(6)Sn-5 phases revealed that the presence of nickel in the tin substrate did not affect the rate of formation/growth of those phases in comparison with the binary Cu/Sn diffusion couples.