NOVELTY - Preparing nano-gold catalysts supported on copper oxide-cerium oxide (CuO-CeO2), comprises preparing CuO-CeO2 by impregnation or coprecipitation methods, preparing an oxide support of CuO-CeO2 by coprecipitation or incipient-wetness impregnation methods, where the coprecipitation method comprises adding copper nitrate and cerium nitrate powders into water, slowly adding ammonia water to precipitate CuO-CeO2, calcining the precipitate in air and grinding the calcined CuO-CeO2 precipitate to obtain CuO-CeO2 powder, and depositing gold particles on the oxide support of CuO-CeO2.    USE - The method is useful for preparing nano-gold catalysts supported on copper oxide-cerium oxide, where the nano-gold catalyst is useful for removing carbon monoxide from a gas stream (all claimed) in fuel cell to prevent the electrode of the fuel cell from poisoning and to increase hydrogen purity in the tank.    ADVANTAGE - The method economically and simply produces nano-gold catalysts with enhanced stability of the gold particle and activity.    DETAILED DESCRIPTION - Preparation of nano-gold catalysts supported on copper oxide-cerium oxide (CuO-CeO2), comprises preparing CuO-CeO2 by impregnation method or coprecipitation method, preparing an oxide support of CuO-CeO2 by coprecipitation method or incipient-wetness impregnation method, where: the coprecipitation method comprises adding copper nitrate and cerium nitrate powders into water to form a solution, slowly adding ammonia water to precipitate CuO-CeO2, calcining the CuO-CeO2 precipitate in air at a temperature of 200-400 degrees C for 2-10 hours and grinding the calcined CuO-CeO2 precipitate to obtain CuO-CeO2 powder; or the incipient-wetness impregnation method comprises adding copper nitrate powder into water to form a solution, dropping the copper nitrate solution into CeO2 and then stirring and calcining the mixture in air at a temperature of 200-400 degrees C for 2-10 hours to obtain CuO-CeO2 powder, and depositing gold particles on the oxide support of CuO-CeO2 by deposition-precipitation method, where the gold solution and CuO-CeO2 are added into water; the solution is controlled at the pH value of 7-9 by ammonia water, stirred for 1-10 hours at a temperature of 50-70 degrees C, washed by distilled water at 50-70 degrees C, dried at 60-80 degrees C for 12 hours, and calcined at 120-200 degrees C for 2-10 hours; the ratio of copper to cerium in the CuO-CeO2 is 1/99 and 50/50; the weight percentage of gold is 0.5-2 wt.%; and the particle size of gold is 1-5 nm. An INDEPENDENT CLAIM is included for removing carbon monoxide from a gas stream comprising applying nano-gold catalysts supported by CuO-CeO2 to the gas stream containing hydrogen to oxidize the carbon monoxide into carbon dioxide (CO2) at a temperature of 20-200 degrees C, where the reaction gas contains oxygen, carbon monoxide and hydrogen and the mole ratio of oxygen/carbon monoxide is 1:4.