Thin films of La1.61GeO5-delta, a new oxide ionic conductor, were fabricated on dense polycrystalline Al2O3 substrates by a pulsed laser deposition (PLD) method and the effect of the film thickness on the oxide ionic conductivity was investigated on the nanoscale. The deposition parameters were optimized to obtain La1.61GeO5-delta thin films with stoichiometric composition. Annealing was found necessary to get crystalline La1.61GeO5-delta thin films. It was also found that the annealed La1.61GeO5-delta film exhibited extraordinarily high oxide ionic conductivity. Due to the nano-size effects, the oxide ion conductivity of La1.61GeO5-delta thin films increased with the decreasing thickness as compared to that in bulk La1.61GeO5-delta. In particular, the improvement in conductivity of the film at low temperature was significant The electrical conductivity of the La1.61GeO5-delta film with a thickness of 373 nm is as high as 0.05 S cm(-1) (log(sigma/S cm(-1)) = -1.3) at 573 K. (c) 2006 Elsevier B.V. All rights reserved.