[en] The effects of extent of competition between H⁺ and Cu²⁺ ions for ion-exchange sites in the Nafion-117 membrane on self-diffusion coefficient of Cu²⁺ ions have been investigated by radiotracer methods. It was observed that there is no significant effects of H⁺ ions on kinetics of isotopic exchange of Cu²⁺ ions up to pH = 2. Therefore, the radiotracer-exchange profiles in the Nafion-117 in the range of 2-4 were used for evaluating self -diffusion coefficient of Cu²⁺ ions in the membrane. The self-diffusion coefficient of Cu²⁺ ions in Nafion-117 membrane was found to be (2.99±0.075)x 10^-7 cm²/sec. Thus, present study demonstrates the possibility of measuring self-diffusion coefficients of ions which hydrolyses at neutral pH. (author)