The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf2N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf2N containing 12 mmol dm(-3) Cu(I) ions was 1.2 x 10(-6) cm(2) s(-1) and the redox potential of Cu(I)/Cu was in the potential range 0.1-0.2 V vs. I-/I-3(-) at 50 degrees C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 x 10(-5) cm(2) s(-1) at 112 degrees C, which was comparable to that of Cu(II) ions in aqueous CuSO4 solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol(-1) in the ionic liquid solution.