In this work, the effects of Ce doping on the Ca and NI) ions in complex perovskite Ba3Ca1.18Nb1.82O9-delta (BCN18) proton conductor have been evaluated. It has been found that cerium ions can be doped into both the Ca and NI) sites to form a single-phase complex perovskite structure when the sintering temperature is 1550 degrees C. Ce ions substituted with Nb ions enhances the electrical conductivity. especially the grain boundary conductivity. The highest conductivity has been obtained for a composition of Ba3Ca1.18Nb1.62Ce0.2O9-delta, possessing a conductivity of 2.69 x 10(-3) S cm(-1) at 550 degrees C in wet H-2. a 78% enhancement compared with BCN18 (1.51 x 10(-3) S cm(-1)). The chemical stability tests show that Ce-doped BCN18 samples remain single phase after treated either in boiling water for 7 h or in pure CO2 for 4 h at 700 degrees C. This work has demonstrated a new direction in developing intermediate temperature proton conducting materials that possess both high conductivity and good stability. (C) 2011 Elsevier B.V. All rights reserved.