Simple transition-metal salts were investigated as the catalysts for the partial oxidation of methane. In trifluoroacetic acid (TFA), methane could be efficiently converted to methyl trifluoroacetate by the Cu(OAc) 2 /K 2 S 2 O 8 catalyst system. A quantitative yield (96.3%) based on methane has been obtained under the optimized conditions. A possible mechanism involving radical intermediates has been suggested for this reaction.