The lithium ion conductivities of perovskite-type oxide La-0.52(1) (Li0.30(1)TiO2.93(2))-Li-6 and La-0.52(1) Li-7(0.30(1)) TiO2.93(2) single crystals, sigma(6) and sigma(7), which were prepared by reproducible isotope exchange process using molten salt, were measured. The sigma(6)/sigma(7) ratio was almost the same as the classical theoretical value, 1.08, and the activation energies of these samples were constant. (C) 2002 The Electrochemical Society.