Three nano-copper-coated iron plates with different thicknesses of the copper coating from 29 to 56 nm were prepared by sputtering and their adhesion properties to rubber compounds were examined. At the optimum cure of rubber, the nano-copper-coated iron plate with thick copper coating (56 nm) showed the best adhesion to rubber compound, whereas the thin copper coating (29 nm) showed the best adhesion to rubber compound at overcure. This may be explained as follows: at optimum cure, diffusion of iron to the copper surface in the adhesion interphase is dominant, whereas copper sulfide formation in the adhesion interphase is dominant at overcure. This fact was confirmed by Auger electron spectroscopy (AES) depth profiles of adhesion interphases using Ar+ ion sputtering.