Determining the relationship between electrical conductivity and doping level in high temperature proton conductors is of great significance to accelerate their process of practicality and develop new applications. In this work, BaCe1-xSmxO3-delta (x = 0.01-0.50) was synthesized via citric-nitrate method and their electrical conduction behavior in 5% H-2/Ar in the intermediate temperature range was investigated. The solubility of Sm in BaCeO3 was between 0.30 and 0.40. Both the bulk and the grain boundary conductivity increased with Sm content up to x = 0.20 and then decreased. The infrared spectra results indicated that the degree of hydrogen bonding decreased with Sm content (x = 0.20-0.30), which should be responsible for the descending bulk conductivity of samples with x = 0.25 and 0.30. BaCe0.80Sm0.20O3-delta, with electrical conductivity of 0.017 S cm(-1) at 600 degrees C, was a promising electrolyte for intermediate temperature solid oxide fuel cells. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.