Oxygen adsorption on the alpha-Mo2C(0 0 0 1) surface has been investigated with valence photoelectron spectroscopy (PES) utilizing synchrotron radiation and X-ray photoelectron spectroscopy (XPS). It is found that the adsorbed oxygen atoms interact both with Mo and C atoms forming an oxycarbide layer on the Mo2C(0 0 0 1) surface. Valence PES study shows that the oxygen adsorption induces a state around the Fermi level, which enhances the emission intensity at the Fermi edge in PES spectra. (C) 2004 Published by Elsevier B.V.