The catalytic properties of gadolinium-doped ceria (CGO) in methane steam reforming were studied. Catalytic tests were carried out between 750 and 900 degrees C, for H2O/CH4 ratios varying between 0.1 and 1, pretreated in H2O/N-2, N-2 and H-2/N-2. Above 800 degrees C, slight deactivation with time on stream was observed except for the H-2-pretreated sample. Surface area measurements, O-2 adsorption at room temperature and O-2-temperature programmed oxidation experiments were performed after catalytic testing. Changes in both surface area and redox properties of CGO were observed and related to catalytic deactivation. Hydrogen is thought to play a key role in catalytic activity and deactivation process. (C) 2008 Elsevier B.V. All rights reserved.