The oxidation of CO in acidic media is very important. For example, in direct methanol fuel cell, CO tends to poison the Pt electrode and cause a reduction of cell output power. CO can be removed by oxidation under the catalysis of Au nanoclusters with an optimal size of 2 nm. However, such small Au clusters tend to be corroded in the acidic media. Here we developed a facile method to solve this problem via hydrophobic carbon coating. The Au@C composite was prepared by reverse microemulsion-hydrothermal method. The hydrophobic carbon can effectively avoid the corrosion of gold nanoclusters by an acid environment while catalyzing CO oxidation efficiently.