Proton concentration as a function of ambient temperature in 15 mol% Y-doped BaZrO3 proton conductors prepared at 1800 degrees C, 1600 degrees C and 1400 degrees C, is measured by thermo-gravimetric (TG) analysis. TG analysis reveals that the maximum proton concentration in the specimen prepared at 1400 degrees C is over 15 mol%. The value is over the limitation decided by hydration process via oxygen vacancy. Infrared diffuse reflection spectroscopy confirms that additional O-D stretching vibration exists in the specimen. Both results strongly suggest that not a few amounts of water incorporate in the specimen prepared at low temperature through other hydration process. (C) 2010 Elsevier B.V. All rights reserved.