Ni/Cu nano-multilayers were fabricated by an electrodeposition technique. Ratio of the Ni:Cu layer thickness was kept at 1:1. By laminating nickel and copper layers at a very narrow spacing, we obtained highly-densified parallel interfaces which can give rise to high strength. Dependence of Vickers hardness and tensile deformation on individual layer thickness h was investigated on the Ni/Cu multilayers. The Vickers hardness increased with decreasing layer thickness for the multilayers of h >= 10 nm. This change in the hardness was consistent with the Hall-Petch relation. At the 10 nm layer thickness, the hardness attained more than three times higher than that of the copper substrate. On the other hand, the hardness decreased rapidly with the layer thickness at h < 10 nm. The tensile deformation tests were also carried out at the substrates coated with the multilayer of h = 5, 20 and 100 nm. The SEM observations revealed that the slip lines of the deformed substrates were terminated by the multilayer at the multilayers of h = 20 and 100 nm. On the other hand, a lot of slip lines penetrated into the multilayer of h = 5 nm. These slip observations were compatible with the layer thickness dependence of the hardness. (c) 2005 Springer Science + Business Media, Inc.