The　adsorption　of　CH2O　at　low-coordinated　sites　(edge　and　corner)　of　MgO　(001)　surface　has　been　studied　using　cluster　models　in　the　framework　of　density　functional　theory.　Two　adsorption　states　of　CH2O,　i.e.　heterolytically　dissociative　adsorption　and　molecular　adsorption　were　found.　In　the　former　case,　the　CH2O　adsorbed　over　Mg-3C-O-3C　pair　site　was　dissociated　into　two　separate　subspecies,　＂CHO-＂　and　＂H+＂　through　the　C-H　bond　cleavage　with　rather　low　activation　energy,　4.58　kcal/mol.　Due　to　the　quite　similarity　in　adsorption　energy,　it　can　be　expected　that　both　two　adsorption　states,　namely　molecular　and　dissociative　adsorption,　should　simultaneously　exist　for　CH2O　over　Mg-3C-O-3C　pair　site　of　MgO　(001)　surface.　In　analogy,　for　CH4,　C2H2　and　CH3OH,　the　edge　and　corner　sites　of　MgO　(001)　surface　exhibit　the　catalytic　reactivity　toward　the　C-H　bond　cleavage,　thus　leading　to　the　dissociative　subspecies,　which　was　reinforced　by　the　quantum　chemical　calculations　and　the　respective　experiments.　(C)　2004　Elsevier　B.V.　All　rights　reserved.