CO oxidation on Au-2n(-) (n = 1 - 4) cluster anions are investigated using DFT methods. O-2 prefers to bind on-top to a gold atom. Binding energies of O-2 on Au-2n(-) are in the range of 0.8-1.2 eV. CO molecule can then insert into the O-O bond of Au2nO2- to form carbonate species, that are the most stable Au2nCO3- isomers, and thus expected to play an important role in CO oxidation. The negative charges of the gold carbonates are mainly distributed on the CO3 moieties. The gold carbonate anions can yield CO2 by direct dissociation or react with another CO to produce 2(CO2). 2010 Elsevier B. V. All rights reserved.