Chemisorption and reactivity of the molecules involved in the water-gas shift (WGS) reaction on gold/ceria catalyst have been studied at 90 and 300 K by FTIR spectroscopy. Forward and reverse WGS reaction at 300 K and up to 573 K have been investigated, too. The FTIR results show that gold causes a strong modification of the surface properties of the support. The nanosized metallic gold particles in close contact with defective ceria play an essential role for the genesis of high catalytic activity in WGS reaction at low temperature and appear to be of crucial importance in explaining the remarkably high stability of this catalytic system. An electronic interaction between small gold metallic nanoparticles and ceria has been evidenced. (C) 2003 Elsevier B.V. All rights reserved.