Ce-supported activated carbon-carbon nanotube composite (Ce/AC-CNTs) catalyst was prepared by in situ formation of CNTs on AC and then modified by Ce. This Ce/AC-CNTs catalyst was subsequently used for low-temperature selective catalytic reduction of NO x with NH 3 (NH 3 -SCR). The NO conversion of Ce/AC-CNTs was 1.41 times higher than that of Ce/AC at 150 °C with good SO 2 tolerance. The catalysts were analyzed by N 2 physisorption, SEM, XRD, NH 3 -TPD, XPS, and Raman technologies. The results showed that the introduction of CNTs could form new mesopores and increase the amount of surface chemisorbed oxygen and acid sites, which all contribute to the high NH 3 -SCR activity.