Decomposition of Freon-12 (CCl2F2) and methyl chloride (CH3Cl) over gold catalysts were studied. Au/Co3O4 showed a high activity for CH3Cl but a lesser activity for CCl2F2 while Au/Al2O3 showed moderate activities for the both reactants. The first step of the reactions over Au/Al2O3 was considered as substitution of Cl by surface OH group on support surface.