The decomposition of methanol on clean and oxygen-precovered CuCl(111) surface have been studied with the method of density functional theory-generalized gradient approximation (DFT-GGA) and the periodic slab models. The effects of different methanol coverages up to one monolayer are investigated. The activation of the O-H bond of methanol to form the methoxide intermediate, the activation of the C-H bond to form the hydroxymethyl intermediate and the activation of the C-O bond to form methyl are examined. These intermediates can subsequently react to form methoxide, hydroxymethyl, methyl, formaldehyde, formyl, and finally CO on the surface. The chemisorption energies of CH3OH, CH3O, H2COH, CH3, H2CO, HCO, OH and CO at their most favorable adsorption sites are predicted to be -57.9, -235.3, -172.9, -170.5, -67.8, -192.4, -309.5 and -105.7 kJ/mol, respectively. We also confirm that the O-H bond-breaking paths have lower energy barrier, compared to the C-O and C-H bond-breaking paths. However, these reactions need a lower energy barrier when precovered oxygen atoms participate in these reactions. (c) 2008 Elsevier B.V. All rights reserved.