The activation of ethanol and methanol by VO2+ in gas phase has been theoretically investigated by using density functional theory (DFT). For the VO2+/ethanol system, the activation energy (Delta E) is found to follow the order of Delta E(C-beta-H) < Delta E(C-alpha-H) approximate to Delta E(O-H). Loss of methyl and glycol occurs respectively via O-H and C-beta-H activation, while acetaldehyde elimination proceeds through two comparable O-H and C-alpha-H activations yielding both VO(H2O)(+) and V(OH)(2)(+). Loss of water not only gives rise to VO(CH3CHO)(+) via both O-H and C-alpha-H activation but also forms VO2(C2H4)(+) via C-beta-H activation. The major product of ethylene is formed via both O-H and C-beta-H activation for yielding VO(OH)(2)(+) and VO2(H2O)(+). In the methanol reaction, both initial O-H and C-alpha-H activation accounts for formaldehyde and water elimination, but the former pathway is preferred.