Abstract: With attapulgite clay (APT) as support, the Pd-Cu/APT catalysts were prepared by an ammonia evaporation method and characterized by N₂-physisorption, XRD, FT-IR, TEM and H₂-TPR. The effect of ammonia concentration on the catalytic performance of Pd-Cu/APT in CO oxidation at room temperature was investigated in a fixed-bed continuous flow microreactor. The results showed that CuO appears as the main Cu species in the Pd-Cu/APT catalysts prepared with over low or over high ammonia concentration, whereas the quantity of Cu₂(OH)₃Cl phase is much less. However, a proper concentration of ammonia is of benefits to forming stable Cu₂(OH)₃Cl species in Pd-Cu/APT; owing to its high dispersion, nano-platelet morphology and strong interaction with Pd species, the presence of stable Cu₂(OH)₃Cl can significantly promote the catalytic performance of Pd-Cu/APT in CO oxidation. Under a gas hourly space velocity (GHSV) of 6 000 h^-1 for a feed stream containing 1.5% CO and 3.3% water, the Pd-Cu/APT catalyst exhibits excellent activity and stability in CO oxidation even at room temperature.