Lithium diffusion coefficients in amorphous lithium phosphate (a-Li3PO4) thin films were determined by secondary ion mass spectroscopy (SIMS), using Li-7 and Li-6 stable isotopes. The diffusion couples were prepared by an ion-exchange method using liquid electrolyte and a mask method based on thin-film deposition. The tracer diffusion coefficient, D-Li*, was evaluated by analyzing the isotope profiles obtained by SIMS in the temperature range of 25-160 degrees C. The diffusion coefficient of a-Li3PO4 was 6.0 x 10(-13) cm(2)/s at 25 degrees C, while the activation energy was 0.58 eV, as measured for the samples prepared by using the ion-exchange method. The conductivity diffusion coefficient, D-sigma, was calculated from the thin film ionic conductivity, which was determined by impedance spectroscopy. The correlation factor, H-R, was 0.55 +/- 0.20 in the measured temperature range, which indicated the cooperative motion of lithium ions in lithium phosphate glasses. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).